build CrOS chrome with gn

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 3eed120832f10c091058706af881c439adc0454c..a7d91acfca613e00c0a924ac1522f50892ebe266 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -181,12 +181,13 @@ if (target_os == "android") {
     _default_toolchain = "//build/toolchain/android:$target_cpu"
   }
 } else if (target_os == "chromeos") {
+  # See comments in build/toolchain/cros/BUILD.gn about board compiles.
   assert(host_os == "linux",
          "ChromeOS builds are only supported on Linux hosts.")
   if (is_clang) {
-    _default_toolchain = "//build/toolchain/linux:clang_$target_cpu"
+    _default_toolchain = "//build/toolchain/cros:clang_$target_cpu"

[Dirk Pranke, 2015/12/02 00:25:17]

If someone tries to do a build with target_os="chromeos" target_cpu="arm",
this'll break.

I suggest we either get rid of the $target_cpu part, or at least assert that
it's == host_cpu .

[rjkroege, 2015/12/03 18:48:59]

Done. And verified that (with the right args.gn) that I can build at least
content shell for ARM

   } else {
-    _default_toolchain = "//build/toolchain/linux:$target_cpu"
+    _default_toolchain = "//build/toolchain/cros:$target_cpu"
   }
 } else if (target_os == "ios") {
   _default_toolchain = "//build/toolchain/mac:ios_clang_arm"