diff --git a/tools/gn/build_settings.cc b/tools/gn/build_settings.cc
index af81467..0a75569 100644
--- a/tools/gn/build_settings.cc
+++ b/tools/gn/build_settings.cc
@@ -46,9 +46,6 @@
 void BuildSettings::SetBuildDir(const SourceDir& d) {
   build_dir_ = d;
   build_to_source_dir_string_ = InvertDir(d);
-
-  DCHECK(!root_path_.empty());
-  file_util::CreateDirectory(build_dir_.Resolve(root_path_));
 }
 
 base::FilePath BuildSettings::GetFullPath(const SourceFile& file) const {
diff --git a/tools/gn/build_settings.h b/tools/gn/build_settings.h
index 231d040..fc175df 100644
--- a/tools/gn/build_settings.h
+++ b/tools/gn/build_settings.h
@@ -60,8 +60,7 @@
 
   // The build directory is the root of all output files. The default toolchain
   // files go into here, and non-default toolchains will have separate
-  // toolchain-specific root directories inside this. This should be set after
-  // the root path for the proper directory to be created.
+  // toolchain-specific root directories inside this.
   const SourceDir& build_dir() const { return build_dir_; }
   void SetBuildDir(const SourceDir& dir);
 
diff --git a/tools/gn/function_exec_script.cc b/tools/gn/function_exec_script.cc
index 540d189..bf55165 100644
--- a/tools/gn/function_exec_script.cc
+++ b/tools/gn/function_exec_script.cc
@@ -348,6 +348,14 @@
 
   base::FilePath startup_dir =
       build_settings->GetFullPath(build_settings->build_dir());
+  // The first time a build is run, no targets will have been written so the
+  // build output directory won't exist. We need to make sure it does before
+  // running any scripts with this as its startup directory, although it will
+  // be relatively rare that the directory won't exist by the time we get here.
+  //
+  // If this shows up on benchmarks, we can cache whether we've done this
+  // or not and skip creating the directory.
+  file_util::CreateDirectory(startup_dir);
 
   // Execute the process.
   // TODO(brettw) set the environment block.
diff --git a/tools/gn/ninja_binary_target_writer_unittest.cc b/tools/gn/ninja_binary_target_writer_unittest.cc
index f57bb19..0bf4722 100644
--- a/tools/gn/ninja_binary_target_writer_unittest.cc
+++ b/tools/gn/ninja_binary_target_writer_unittest.cc
@@ -1,89 +1,87 @@
-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include <sstream>
-
-#include "testing/gtest/include/gtest/gtest.h"
-#include "tools/gn/ninja_binary_target_writer.h"
-#include "tools/gn/test_with_scope.h"
-
-TEST(NinjaBinaryTargetWriter, SourceSet) {
-  TestWithScope setup;
-  setup.build_settings()->SetBuildDir(SourceDir("//out/Debug/"));
-  setup.settings()->set_target_os(Settings::WIN);
-
-  Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
-  target.set_output_type(Target::SOURCE_SET);
-  target.sources().push_back(SourceFile("//foo/input1.cc"));
-  target.sources().push_back(SourceFile("//foo/input2.cc"));
-  target.OnResolved();
-
-  // Source set itself.
-  {
-    std::ostringstream out;
-    NinjaBinaryTargetWriter writer(&target, out);
-    writer.Run();
-
-    // TODO(brettw) I think we'll need to worry about backslashes here
-    // depending if we're on actual Windows or Linux pretending to be Windows.
-    const char expected_win[] =
-        "arch = environment.x86\n"
-        "defines =\n"
-        "includes =\n"
-        "cflags =\n"
-        "cflags_c =\n"
-        "cflags_cc =\n"
-        "cflags_objc =\n"
-        "cflags_objcc =\n"
-        "\n"
-        "build obj/foo/bar.input1.obj: tc_cxx ../../foo/input1.cc\n"
-        "build obj/foo/bar.input2.obj: tc_cxx ../../foo/input2.cc\n"
-        "\n"
-        "build obj/foo/bar.stamp: tc_stamp obj/foo/bar.input1.obj obj/foo/bar.input2.obj\n";
-    std::string out_str = out.str();
-#if defined(OS_WIN)
-    std::replace(out_str.begin(), out_str.end(), '\\', '/');
-#endif
-    EXPECT_EQ(expected_win, out_str);
-  }
-
-  // A shared library that depends on the source set.
-  Target shlib_target(setup.settings(), Label(SourceDir("//foo/"), "shlib"));
-  shlib_target.set_output_type(Target::SHARED_LIBRARY);
-  shlib_target.deps().push_back(&target);
-  shlib_target.OnResolved();
-
-  {
-    std::ostringstream out;
-    NinjaBinaryTargetWriter writer(&shlib_target, out);
-    writer.Run();
-
-    // TODO(brettw) I think we'll need to worry about backslashes here
-    // depending if we're on actual Windows or Linux pretending to be Windows.
-    const char expected_win[] =
-        "arch = environment.x86\n"
-        "defines =\n"
-        "includes =\n"
-        "cflags =\n"
-        "cflags_c =\n"
-        "cflags_cc =\n"
-        "cflags_objc =\n"
-        "cflags_objcc =\n"
-        "\n"
-        "\n"
-        "manifests = obj/foo/shlib.intermediate.manifest\n"
-        "ldflags = /MANIFEST /ManifestFile:obj/foo/shlib.intermediate.manifest\n"
-        "libs =\n"
-        "build shlib.dll shlib.dll.lib: tc_solink obj/foo/bar.input1.obj obj/foo/bar.input2.obj\n"
-        "  soname = shlib.dll\n"
-        "  lib = shlib.dll\n"
-        "  dll = shlib.dll\n"
-        "  implibflag = /IMPLIB:shlib.dll.lib\n\n";
-    std::string out_str = out.str();
-#if defined(OS_WIN)
-    std::replace(out_str.begin(), out_str.end(), '\\', '/');
-#endif
-    EXPECT_EQ(expected_win, out_str);
-  }
-}
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <sstream>
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/ninja_binary_target_writer.h"
+#include "tools/gn/test_with_scope.h"
+
+TEST(NinjaBinaryTargetWriter, SourceSet) {
+  TestWithScope setup;
+  setup.build_settings()->SetBuildDir(SourceDir("//out/Debug/"));
+  setup.settings()->set_target_os(Settings::WIN);
+
+  Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
+  target.set_output_type(Target::SOURCE_SET);
+  target.sources().push_back(SourceFile("//foo/input1.cc"));
+  target.sources().push_back(SourceFile("//foo/input2.cc"));
+  target.OnResolved();
+
+  // Source set itself.
+  {
+    std::ostringstream out;
+    NinjaBinaryTargetWriter writer(&target, out);
+    writer.Run();
+
+    // TODO(brettw) I think we'll need to worry about backslashes here
+    // depending if we're on actual Windows or Linux pretending to be Windows.
+    const char expected_win[] =
+        "defines =\n"
+        "includes =\n"
+        "cflags =\n"
+        "cflags_c =\n"
+        "cflags_cc =\n"
+        "cflags_objc =\n"
+        "cflags_objcc =\n"
+        "\n"
+        "build obj/foo/bar.input1.obj: tc_cxx ../../foo/input1.cc\n"
+        "build obj/foo/bar.input2.obj: tc_cxx ../../foo/input2.cc\n"
+        "\n"
+        "build obj/foo/bar.stamp: tc_stamp obj/foo/bar.input1.obj obj/foo/bar.input2.obj\n";
+    std::string out_str = out.str();
+#if defined(OS_WIN)
+    std::replace(out_str.begin(), out_str.end(), '\\', '/');
+#endif
+    EXPECT_EQ(expected_win, out_str);
+  }
+
+  // A shared library that depends on the source set.
+  Target shlib_target(setup.settings(), Label(SourceDir("//foo/"), "shlib"));
+  shlib_target.set_output_type(Target::SHARED_LIBRARY);
+  shlib_target.deps().push_back(&target);
+  shlib_target.OnResolved();
+
+  {
+    std::ostringstream out;
+    NinjaBinaryTargetWriter writer(&shlib_target, out);
+    writer.Run();
+
+    // TODO(brettw) I think we'll need to worry about backslashes here
+    // depending if we're on actual Windows or Linux pretending to be Windows.
+    const char expected_win[] =
+        "defines =\n"
+        "includes =\n"
+        "cflags =\n"
+        "cflags_c =\n"
+        "cflags_cc =\n"
+        "cflags_objc =\n"
+        "cflags_objcc =\n"
+        "\n"
+        "\n"
+        "manifests = obj/foo/shlib.intermediate.manifest\n"
+        "ldflags = /MANIFEST /ManifestFile:obj/foo/shlib.intermediate.manifest\n"
+        "libs =\n"
+        "build shlib.dll shlib.dll.lib: tc_solink obj/foo/bar.input1.obj obj/foo/bar.input2.obj\n"
+        "  soname = shlib.dll\n"
+        "  lib = shlib.dll\n"
+        "  dll = shlib.dll\n"
+        "  implibflag = /IMPLIB:shlib.dll.lib\n\n";
+    std::string out_str = out.str();
+#if defined(OS_WIN)
+    std::replace(out_str.begin(), out_str.end(), '\\', '/');
+#endif
+    EXPECT_EQ(expected_win, out_str);
+  }
+}
diff --git a/tools/gn/ninja_script_target_writer.cc b/tools/gn/ninja_script_target_writer.cc
index b362976..5dd8095 100644
--- a/tools/gn/ninja_script_target_writer.cc
+++ b/tools/gn/ninja_script_target_writer.cc
@@ -75,7 +75,11 @@
     out_ << "rule " << custom_rule_name << std::endl;
     out_ << "  command = ";
     path_output_.WriteFile(out_, settings_->build_settings()->python_path());
-    out_ << " gyp-win-tool action-wrapper $arch " << rspfile << std::endl;
+    // TODO(brettw) this hardcodes "environment.x86" which is something that
+    // the Chrome Windows toolchain writes. We should have a way to invoke
+    // python without requiring this gyp_win_tool thing.
+    out_ << " gyp-win-tool action-wrapper environment.x86 " << rspfile
+         << std::endl;
     out_ << "  description = CUSTOM " << target_label << std::endl;
     out_ << "  restat = 1" << std::endl;
     out_ << "  rspfile = " << rspfile << std::endl;
diff --git a/tools/gn/ninja_script_target_writer_unittest.cc b/tools/gn/ninja_script_target_writer_unittest.cc
index 2057f07..f3e7bf1 100644
--- a/tools/gn/ninja_script_target_writer_unittest.cc
+++ b/tools/gn/ninja_script_target_writer_unittest.cc
@@ -126,9 +126,8 @@
     // TODO(brettw) I think we'll need to worry about backslashes here
     // depending if we're on actual Windows or Linux pretending to be Windows.
     const char expected_win[] =
-        "arch = environment.x86\n"
         "rule __foo_bar___rule\n"
-        "  command = C:/python/python.exe gyp-win-tool action-wrapper $arch __foo_bar___rule.$unique_name.rsp\n"
+        "  command = C:/python/python.exe gyp-win-tool action-wrapper environment.x86 __foo_bar___rule.$unique_name.rsp\n"
         "  description = CUSTOM //foo:bar()\n"
         "  restat = 1\n"
         "  rspfile = __foo_bar___rule.$unique_name.rsp\n"
diff --git a/tools/gn/secondary/BUILD.gn b/tools/gn/secondary/BUILD.gn
index d285eb4..7a4f786 100644
--- a/tools/gn/secondary/BUILD.gn
+++ b/tools/gn/secondary/BUILD.gn
@@ -9,6 +9,7 @@
     "//base(//build/toolchain/nacl:x86_newlib)",
     "//chrome",
     "//crypto",
+    "//device/usb:device_usb",
     "//ipc",
     "//net",
     "//net/third_party/nss:ssl",
diff --git a/tools/gn/secondary/device/usb/BUILD.gn b/tools/gn/secondary/device/usb/BUILD.gn
new file mode 100644
index 0000000..afe95dc
--- /dev/null
+++ b/tools/gn/secondary/device/usb/BUILD.gn
@@ -0,0 +1,25 @@
+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_ids = "//third_party/usb_ids/usb.ids"
+generated_ids = "$target_gen_dir/usb_ids_gen.cc"
+
+static_library("device_usb") {
+  sources = [
+    "usb_ids.cc",
+    "usb_ids.h",
+    generated_ids,
+  ]
+  deps = [ ":device_usb_ids" ]
+}
+
+custom("device_usb_ids") {
+  script = "//tools/usb_ids/usb_ids.py"
+  source_prereqs = [ source_ids ]
+  outputs = [ generated_ids ]
+  args = [
+    "-i", rebase_path(source_ids, ".", root_build_dir),
+    "-o", rebase_path(generated_ids, ".", root_build_dir),
+  ]
+}