diff --git a/infra/README.recipes.md b/infra/README.recipes.md
index 8ee6bd2..7e43239 100644
--- a/infra/README.recipes.md
+++ b/infra/README.recipes.md
@@ -8,15 +8,16 @@
 
 ### *recipes* / [gn](/infra/recipes/gn.py)
 
-[DEPS](/infra/recipes/gn.py#6): [recipe\_engine/buildbucket][recipe_engine/recipe_modules/buildbucket], [recipe\_engine/cipd][recipe_engine/recipe_modules/cipd], [recipe\_engine/context][recipe_engine/recipe_modules/context], [recipe\_engine/path][recipe_engine/recipe_modules/path], [recipe\_engine/platform][recipe_engine/recipe_modules/platform], [recipe\_engine/properties][recipe_engine/recipe_modules/properties], [recipe\_engine/python][recipe_engine/recipe_modules/python], [recipe\_engine/step][recipe_engine/recipe_modules/step]
+[DEPS](/infra/recipes/gn.py#6): [recipe\_engine/buildbucket][recipe_engine/recipe_modules/buildbucket], [recipe\_engine/cipd][recipe_engine/recipe_modules/cipd], [recipe\_engine/context][recipe_engine/recipe_modules/context], [recipe\_engine/json][recipe_engine/recipe_modules/json], [recipe\_engine/path][recipe_engine/recipe_modules/path], [recipe\_engine/platform][recipe_engine/recipe_modules/platform], [recipe\_engine/properties][recipe_engine/recipe_modules/properties], [recipe\_engine/python][recipe_engine/recipe_modules/python], [recipe\_engine/step][recipe_engine/recipe_modules/step]
 
 Recipe for building GN.
 
-&mdash; **def [RunSteps](/infra/recipes/gn.py#18)(api):**
+&mdash; **def [RunSteps](/infra/recipes/gn.py#19)(api):**
 
 [recipe_engine/recipe_modules/buildbucket]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-buildbucket
 [recipe_engine/recipe_modules/cipd]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-cipd
 [recipe_engine/recipe_modules/context]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-context
+[recipe_engine/recipe_modules/json]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-json
 [recipe_engine/recipe_modules/path]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-path
 [recipe_engine/recipe_modules/platform]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-platform
 [recipe_engine/recipe_modules/properties]: https://chromium.googlesource.com/infra/luci/recipes-py.git/+/40699af88c76d65ef1b3d364de221611603e2dc6/README.recipes.md#recipe_modules-properties
diff --git a/infra/recipes/gn.expected/ci_win.json b/infra/recipes/gn.expected/ci_win.json
index b69295b..ddcdc94 100644
--- a/infra/recipes/gn.expected/ci_win.json
+++ b/infra/recipes/gn.expected/ci_win.json
@@ -49,7 +49,7 @@
       "-root",
       "[START_DIR]\\cipd",
       "-ensure-file",
-      "infra/ninja/${platform} version:1.8.2",
+      "chrome_internal/third_party/sdk/windows latest\ninfra/ninja/${platform} version:1.8.2",
       "-json-output",
       "/path/to/tmp/json"
     ],
@@ -60,6 +60,10 @@
       "@@@STEP_LOG_LINE@json.output@  \"result\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"\": [@@@",
       "@@@STEP_LOG_LINE@json.output@      {@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"instance_id\": \"resolved-instance_id-of-latest----------\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"package\": \"chrome_internal/third_party/sdk/windows\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      }, @@@",
+      "@@@STEP_LOG_LINE@json.output@      {@@@",
       "@@@STEP_LOG_LINE@json.output@        \"instance_id\": \"resolved-instance_id-of-version:1.8.2---\", @@@",
       "@@@STEP_LOG_LINE@json.output@        \"package\": \"infra/ninja/${platform}\"@@@",
       "@@@STEP_LOG_LINE@json.output@      }@@@",
@@ -70,6 +74,76 @@
     ]
   },
   {
+    "cmd": [
+      "python",
+      "-u",
+      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "[START_DIR]\\cipd\\win_sdk\\bin\\SetEnv.x64.json",
+      "/path/to/tmp/json"
+    ],
+    "name": "SetEnv.x64.json",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@json.output@{@@@",
+      "@@@STEP_LOG_LINE@json.output@  \"env\": {@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"INCLUDE\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"um\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"shared\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"winrt\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ], @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"PATH\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"bin\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"x64\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"VC\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Tools\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"MSVC\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"14.14.26428\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"bin\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"HostX64\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"x64\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ], @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"VSINSTALLDIR\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\\\\\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ]@@@",
+      "@@@STEP_LOG_LINE@json.output@  }@@@",
+      "@@@STEP_LOG_LINE@json.output@}@@@",
+      "@@@STEP_LOG_END@json.output@@@"
+    ]
+  },
+  {
     "cmd": [],
     "name": "debug"
   },
@@ -88,6 +162,16 @@
       "-d"
     ],
     "cwd": "[START_DIR]\\gn",
+    "env": {
+      "INCLUDE": "[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\um;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\shared;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\winrt",
+      "VSINSTALLDIR": "[START_DIR]\\cipd"
+    },
+    "env_prefixes": {
+      "PATH": [
+        "[START_DIR]\\cipd\\win_sdk\\bin\\10.0.17134.0\\x64",
+        "[START_DIR]\\cipd\\VC\\Tools\\MSVC\\14.14.26428\\bin\\HostX64\\x64"
+      ]
+    },
     "name": "debug.build.generate",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@2@@@"
@@ -132,6 +216,16 @@
       "[START_DIR]\\gn\\build\\gen.py"
     ],
     "cwd": "[START_DIR]\\gn",
+    "env": {
+      "INCLUDE": "[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\um;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\shared;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\winrt",
+      "VSINSTALLDIR": "[START_DIR]\\cipd"
+    },
+    "env_prefixes": {
+      "PATH": [
+        "[START_DIR]\\cipd\\win_sdk\\bin\\10.0.17134.0\\x64",
+        "[START_DIR]\\cipd\\VC\\Tools\\MSVC\\14.14.26428\\bin\\HostX64\\x64"
+      ]
+    },
     "name": "release.build.generate",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@2@@@"
diff --git a/infra/recipes/gn.expected/cq_win.json b/infra/recipes/gn.expected/cq_win.json
index b1beb7e..b3f46ba 100644
--- a/infra/recipes/gn.expected/cq_win.json
+++ b/infra/recipes/gn.expected/cq_win.json
@@ -76,7 +76,7 @@
       "-root",
       "[START_DIR]\\cipd",
       "-ensure-file",
-      "infra/ninja/${platform} version:1.8.2",
+      "chrome_internal/third_party/sdk/windows latest\ninfra/ninja/${platform} version:1.8.2",
       "-json-output",
       "/path/to/tmp/json"
     ],
@@ -87,6 +87,10 @@
       "@@@STEP_LOG_LINE@json.output@  \"result\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"\": [@@@",
       "@@@STEP_LOG_LINE@json.output@      {@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"instance_id\": \"resolved-instance_id-of-latest----------\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"package\": \"chrome_internal/third_party/sdk/windows\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      }, @@@",
+      "@@@STEP_LOG_LINE@json.output@      {@@@",
       "@@@STEP_LOG_LINE@json.output@        \"instance_id\": \"resolved-instance_id-of-version:1.8.2---\", @@@",
       "@@@STEP_LOG_LINE@json.output@        \"package\": \"infra/ninja/${platform}\"@@@",
       "@@@STEP_LOG_LINE@json.output@      }@@@",
@@ -97,6 +101,76 @@
     ]
   },
   {
+    "cmd": [
+      "python",
+      "-u",
+      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "[START_DIR]\\cipd\\win_sdk\\bin\\SetEnv.x64.json",
+      "/path/to/tmp/json"
+    ],
+    "name": "SetEnv.x64.json",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@json.output@{@@@",
+      "@@@STEP_LOG_LINE@json.output@  \"env\": {@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"INCLUDE\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"um\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"shared\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Include\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"winrt\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ], @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"PATH\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"win_sdk\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"bin\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"10.0.17134.0\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"x64\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ], @@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"VC\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"Tools\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"MSVC\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"14.14.26428\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"bin\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"HostX64\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"x64\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ], @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"VSINSTALLDIR\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@      [@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\", @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"..\\\\\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      ]@@@",
+      "@@@STEP_LOG_LINE@json.output@    ]@@@",
+      "@@@STEP_LOG_LINE@json.output@  }@@@",
+      "@@@STEP_LOG_LINE@json.output@}@@@",
+      "@@@STEP_LOG_END@json.output@@@"
+    ]
+  },
+  {
     "cmd": [],
     "name": "debug"
   },
@@ -115,6 +189,16 @@
       "-d"
     ],
     "cwd": "[START_DIR]\\gn",
+    "env": {
+      "INCLUDE": "[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\um;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\shared;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\winrt",
+      "VSINSTALLDIR": "[START_DIR]\\cipd"
+    },
+    "env_prefixes": {
+      "PATH": [
+        "[START_DIR]\\cipd\\win_sdk\\bin\\10.0.17134.0\\x64",
+        "[START_DIR]\\cipd\\VC\\Tools\\MSVC\\14.14.26428\\bin\\HostX64\\x64"
+      ]
+    },
     "name": "debug.build.generate",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@2@@@"
@@ -159,6 +243,16 @@
       "[START_DIR]\\gn\\build\\gen.py"
     ],
     "cwd": "[START_DIR]\\gn",
+    "env": {
+      "INCLUDE": "[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\um;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\shared;[START_DIR]\\cipd\\win_sdk\\Include\\10.0.17134.0\\winrt",
+      "VSINSTALLDIR": "[START_DIR]\\cipd"
+    },
+    "env_prefixes": {
+      "PATH": [
+        "[START_DIR]\\cipd\\win_sdk\\bin\\10.0.17134.0\\x64",
+        "[START_DIR]\\cipd\\VC\\Tools\\MSVC\\14.14.26428\\bin\\HostX64\\x64"
+      ]
+    },
     "name": "release.build.generate",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@2@@@"
diff --git a/infra/recipes/gn.py b/infra/recipes/gn.py
index 81d3f07..212cd96 100644
--- a/infra/recipes/gn.py
+++ b/infra/recipes/gn.py
@@ -7,6 +7,7 @@
     'recipe_engine/buildbucket',
     'recipe_engine/cipd',
     'recipe_engine/context',
+    'recipe_engine/json',
     'recipe_engine/path',
     'recipe_engine/platform',
     'recipe_engine/properties',
@@ -48,10 +49,51 @@
             'fuchsia/clang/${platform}': 'goma',
         },
         'mac': {},
-        'win': {},
+        'win': {
+            'chrome_internal/third_party/sdk/windows': 'uploaded:2018-06-13',
+        },
     }[api.platform.name])
     api.cipd.ensure(cipd_dir, packages)
 
+  environ_pre = {}
+
+  win_env = {}
+  if api.platform.name == 'win':
+    # Load .../win_sdk/bin/SetEnv.x64.json to extract the required environment.
+    # It contains a dict that looks like this:
+    # {
+    #   "env": {
+    #     "VAR": [["..", "..", "x"], ["..", "..", "y"]],
+    #     ...
+    #   }
+    # }
+    # All these environment variables need to be added to the environment
+    # for the compiler and linker to work.
+
+    json_file = cipd_dir.join('win_sdk', 'bin', 'SetEnv.x64.json')
+    env = api.json.read('SetEnv.x64.json', json_file).json.output.get('env')
+    for k in env:
+      # recipes' Path() does not like .., ., \, or /, so this is cumbersome.
+      # What we want to do is:
+      #   [sdk_bin_dir.join(*e) for e in env[k]]
+      # Instead do that badly, and rely (but verify) on the fact that the paths
+      # are all specified relative to the root, but specified relative to
+      # win_sdk/bin (i.e. everything starts with "../../".)
+      results = []
+      for data in env[k]:
+        assert data[0] == '..' and (data[1] == '..' or data[1] == '..\\')
+        root_relative = data[2:]
+        results.append('%s' % cipd_dir.join(*root_relative))
+
+      # PATH is special-cased because we don't want to overwrite other things
+      # like C:\Windows\System32. Others are replacements because prepending
+      # doesn't necessarily makes sense, like VSINSTALLDIR.
+      if k.lower() == 'path':
+        # env_prefixes wants a list, not a string like env.
+        environ_pre[k] = results
+      else:
+        win_env[k] = ';'.join(results)
+
   environ = {
       'linux': {
           'CC': cipd_dir.join('bin', 'clang'),
@@ -60,7 +102,7 @@
           'LDFLAGS': '-static-libstdc++ -ldl -lpthread',
       },
       'mac': {},
-      'win': {},
+      'win': win_env,
   }[api.platform.name]
 
   configs = [
@@ -77,7 +119,7 @@
   for config in configs:
     with api.step.nest(config['name']):
       with api.step.nest('build'):
-        with api.context(env=environ, cwd=src_dir):
+        with api.context(env=environ, env_prefixes=environ_pre, cwd=src_dir):
           api.python('generate',
                      src_dir.join('build', 'gen.py'),
                      args=config['args'])
@@ -89,22 +131,37 @@
 
 
 def GenTests(api):
+  WIN_TOOLCHAIN_DATA = {
+    "env": {
+      "VSINSTALLDIR": [["..", "..\\"]],
+      "INCLUDE": [["..", "..", "win_sdk", "Include", "10.0.17134.0", "um"], ["..", "..", "win_sdk", "Include", "10.0.17134.0", "shared"], ["..", "..", "win_sdk", "Include", "10.0.17134.0", "winrt"]],
+      "PATH": [["..", "..", "win_sdk", "bin", "10.0.17134.0", "x64"], ["..", "..", "VC", "Tools", "MSVC", "14.14.26428", "bin", "HostX64", "x64"]],
+    }
+  }
   for platform in ('linux', 'mac', 'win'):
-    yield (api.test('ci_' + platform) + api.platform.name(platform) +
-           api.properties(buildbucket={
-               'build': {
-                   'tags': [
-                       'buildset:commit/gitiles/gn.googlesource.com/gn/+/'
-                       'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
-                   ]
-               }
-           }))
-    yield (
-        api.test('cq_' + platform) + api.platform.name(platform) +
-        api.properties(buildbucket={
-            'build': {
-                'tags': [
-                    'buildset:patch/gerrit/gn-review.googlesource.com/1000/1',
-                ]
-            }
-        }))
+    to_yield = (api.test('ci_' + platform) + api.platform.name(platform) +
+                api.properties(buildbucket={
+                  'build': {
+                    'tags': [
+                      'buildset:commit/gitiles/gn.googlesource.com/gn/+/'
+                      'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
+                    ]
+                  }
+                }))
+    if platform == 'win':
+      to_yield += api.override_step_data('SetEnv.x64.json',
+          api.json.output(WIN_TOOLCHAIN_DATA))
+    yield to_yield
+
+    to_yield = (api.test('cq_' + platform) + api.platform.name(platform) +
+                api.properties(buildbucket={
+                  'build': {
+                    'tags': [
+                      'buildset:patch/gerrit/gn-review.googlesource.com/1000/1',
+                    ]
+                  }
+                }))
+    if platform == 'win':
+      to_yield += api.override_step_data('SetEnv.x64.json',
+          api.json.output(WIN_TOOLCHAIN_DATA))
+    yield to_yield