Make goma work on win GN builds.

build/toolchain/win/BUILD.gn

 # 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.
 
+declare_args() {
+  # Path to the directory containing the VC binaries for the right
+  # combination of host and target architectures. Currently only the
+  # 64-bit host toolchain is supported, with either 32-bit or 64-bit targets.
+  vc_bin_dir = ""
+}
+
 import("//build/config/win/visual_studio_version.gni")
 import("//build/toolchain/goma.gni")
 
 # Should only be running on Windows.
 assert(is_win)
 
 # Setup the Visual Studio state.
 #
 # Its arguments are the VS path and the compiler wrapper tool. It will write
 # "environment.x86" and "environment.x64" to the build directory and return a
 # list to us.
 gyp_win_tool_path = rebase_path("//tools/gyp/pylib/gyp/win_tool.py",
                                 root_build_dir)
-exec_script("setup_toolchain.py",
-            [
-              visual_studio_path,
-              gyp_win_tool_path,
-              windows_sdk_path,
-              visual_studio_runtime_dirs
-            ])
+
+toolchain_data = exec_script("setup_toolchain.py",
+                             [visual_studio_path,
+                              gyp_win_tool_path,
+                              windows_sdk_path,
+                              visual_studio_runtime_dirs,
+                              cpu_arch],
+                             "scope")
+
+if (vc_bin_dir == "") {
+  vc_bin_dir = toolchain_data.vc_bin_dir
+}
 
 # This value will be inherited in the toolchain below.
 concurrent_links = exec_script("../get_concurrent_links.py", [], "value")
 
 # Parameters:
 #  cpu_arch: cpu_arch to pass as a build arg
 #  environment: File name of environment file.
 template("msvc_toolchain") {
   if (defined(invoker.concurrent_links)) {
     concurrent_links = invoker.concurrent_links
   }
 
   env = invoker.environment
 
   if (is_debug) {
     configuration = "Debug"
   } else {
     configuration = "Release"
   }
   exec_script("../../vs_toolchain.py", ["copy_dlls",
                                         rebase_path(root_build_dir),
                                         configuration,
                                         invoker.cpu_arch])
 
+  if (use_goma) {
+    goma_prefix = "$goma_dir/gomacc.exe "
+  } else {
+    goma_prefix = ""
+  }
+
+  cl = "${goma_prefix}\"${vc_bin_dir}/cl.exe\""
+
   toolchain(target_name) {
     # Make these apply to all tools below.
     lib_switch = ""
     lib_dir_switch="/LIBPATH:"
 
     tool("cc") {
       rspfile = "{{output}}.rsp"
       pdbname = "{{target_out_dir}}/{{target_output_name}}_c.pdb"
-      command = "ninja -t msvc -e $env -- cl.exe /nologo /showIncludes /FC @$rspfile /c {{source}} /Fo{{output}} /Fd$pdbname"
+      command = "ninja -t msvc -e $env -- $cl /nologo /showIncludes /FC @$rspfile /c {{source}} /Fo{{output}} /Fd$pdbname"
       depsformat = "msvc"
       description = "CC {{output}}"
       outputs = [
         "{{source_out_dir}}/{{target_output_name}}.{{source_name_part}}.obj",
       ]
       rspfile_content = "{{defines}} {{include_dirs}} {{cflags}} {{cflags_c}}"
     }
 
     tool("cxx") {
       rspfile = "{{output}}.rsp"
       # The PDB name needs to be different between C and C++ compiled files.
       pdbname = "{{target_out_dir}}/{{target_output_name}}_cc.pdb"
-      command = "ninja -t msvc -e $env -- cl.exe /nologo /showIncludes /FC @$rspfile /c {{source}} /Fo{{output}} /Fd$pdbname"
+      command = "ninja -t msvc -e $env -- $cl /nologo /showIncludes /FC @$rspfile /c {{source}} /Fo{{output}} /Fd$pdbname"
       depsformat = "msvc"
       description = "CXX {{output}}"
       outputs = [
         "{{source_out_dir}}/{{target_output_name}}.{{source_name_part}}.obj",
       ]
       rspfile_content = "{{defines}} {{include_dirs}} {{cflags}} {{cflags_c}}"
     }
 
     tool("rc") {
       command = "$python_path gyp-win-tool rc-wrapper $env rc.exe {{defines}} {{include_dirs}} /fo{{output}} {{source}}"
@@ skipping 101 matching lines @@
     cpu_arch = "x86"
   }
 }
 
 if (cpu_arch == "x64") {
   msvc_toolchain("64") {
     environment = "environment.x64"
     cpu_arch = "x64"
   }
 }