Pass enable_themes to grit and use for html conditions regarding themes.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1137 matching lines @@
       }],
       ['OS=="mac"', {
         'grit_defines': ['-D', 'scale_factors=2x'],
       }],
       ['enable_extensions==1', {
         'grit_defines': ['-D', 'enable_extensions'],
       }],
       ['enable_printing==1', {
         'grit_defines': ['-D', 'enable_printing'],
       }],
+      ['enable_themes==1', {
+        'grit_defines': ['-D', 'enable_themes'],
+      }],
       ['clang_use_chrome_plugins==1 and OS!="win"', {
         'clang_chrome_plugins_flags': [
           '<!@(<(DEPTH)/tools/clang/scripts/plugin_flags.sh)'
         ],
       }],
 
       ['enable_web_intents_tag==1', {
         'grit_defines': ['-D', 'enable_web_intents_tag'],
       }],
 
@@ skipping 2165 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }