Setup cache for macOS and Windows SDK

This defines a named cache to hold the SDK for each platform.

Change-Id: Ie0a0f923baa0a7cfacf9ac4a990e20de668b318b
Reviewed-on: https://gn-review.googlesource.com/c/2961
Reviewed-by: Scott Graham <scottmg@chromium.org>

cr-buildbucket.cfg

diff --git a/cr-buildbucket.cfg b/cr-buildbucket.cfg
index 381ab82..03d0dc8 100644
--- a/cr-buildbucket.cfg
+++ b/cr-buildbucket.cfg
@@ -34,6 +34,22 @@
   }
 }
 
+builder_mixins {
+  name: "mac_caches"
+  caches {
+    path: "macos_sdk"
+    name: "macos_sdk"
+  }
+}
+
+builder_mixins {
+  name: "windows_caches"
+  caches {
+    path: "windows_sdk"
+    name: "windows_sdk"
+  }
+}
+
 buckets {
   name: "luci.gn.ci"
   acl_sets: "public"
@@ -64,12 +80,14 @@
       name: "mac"
       dimensions: "os:Mac-10.13"
       dimensions: "cpu:x86-64"
+      mixins: "mac_caches"
     }
 
     builders {
       name: "win"
       dimensions: "os:Windows-10"
       dimensions: "cpu:x86-64"
+      mixins: "windows_caches"
     }
   }
 }
@@ -104,12 +122,14 @@
       name: "mac"
       dimensions: "os:Mac-10.13"
       dimensions: "cpu:x86-64"
+      mixins: "mac_caches"
     }
 
     builders {
       name: "win"
       dimensions: "os:Windows-10"
       dimensions: "cpu:x86-64"
+      mixins: "windows_caches"
     }
   }
 }