Add a wrapper for grit_action.gypi for chrome specific variables.

This makes it easier to add custom grit_additional_defines variable
values in addition to the chrome-default values.

Review URL: https://codereview.chromium.org/1555803002

Cr-Commit-Position: refs/heads/master@{#367471}

chrome/chrome_features.gypi

 # Copyright 2015 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.
- 
+
 # This is the GYP equivalent of //chrome/common/features.gni.
 # Please keep in sync!
 
@@ -38,6 +38,6 @@
     'chrome_grit_defines': [
       '-D', 'enable_google_now=<(enable_google_now)',
       '-D', 'use_vulcanize=<(use_vulcanize)',
-    ]
+    ],
   },
 }

chrome/chrome_grit_action.gypi

+# Copyright 2015 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.
+
+{
+  'variables': {
+    # Wrapper around build/grit_action.gypi that applies Chrome-specific grit
+    # settings. Actions that include this gypi file at their local scopes can
+    # define variables with the same names as the ones below and they will be
+    # merged.
+    'grit_additional_defines': [ '<@(chrome_grit_defines)' ],
+  },
+  'includes': [ '../build/grit_action.gypi', 'chrome_features.gypi' ],
+}