Hook up clang_use_chrome_plugins to the GN build.

build/gyp_chromium

 #!/usr/bin/env python
 
 # 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.
 
 # This script is wrapper for Chromium that adds some support for how GYP
 # is invoked by Chromium beyond what can be done in the gclient hooks.
 
 import glob
@@ skipping 146 matching lines @@
   vars_dict = GetGypVarsForGN(supplemental_files)
   gn_args = ''
 
   # Note: These are the additional flags passed to various builds by builders
   # on the main waterfall. We'll probably need to add these at some point:
   #   mac_strip_release=1         http://crbug.com/330301
   #   linux_dump_symbols=0        http://crbug.com/330300
   #   host_os=linux  Probably can skip, GN knows the host OS.
   #   order_text_section=<path>   http://crbug.com/330299
   #   chromium_win_pch=0          http://crbug.com/297678
-  #   clang_use_chrome_plugins=1  http://crbug.com/330298
   #   chromium_ios_signing=0      http://crbug.com/330302
   #   linux_use_tcmalloc=0        http://crbug.com/330303
   #   release_extra_flags=...     http://crbug.com/330305
 
   # These tuples of (key, value, gn_arg_string) use the gn_arg_string for
   # gn when the key is set to the given value in the GYP arguments.
   remap_cases = [
       ('android_webview_build', '1', 'is_android_webview_build=true'),
       ('branding', 'Chrome', 'is_chrome_branded=true'),
       ('buildtype', 'Official', 'is_official_build=true'),
       ('component', 'shared_library', 'is_component_build=true'),
       ('clang', '1', 'is_clang=true'),
+      ('clang_use_chrome_plugins', '0', 'clang_use_chrome_plugins=false'),
       ('disable_glibcxx_debug', '1', 'disable_glibcxx_debug=true'),
       ('target_arch', 'ia32', 'cpu_arch="x86"'),
       ('target_arch', 'x64', 'cpu_arch="x64" force_win64=true'),
       ('target_arch', 'arm', 'cpu_arch="arm"'),
       ('target_arch', 'mipsel', 'cpu_arch="mipsel"'),
       ('fastbuild', '0', 'symbol_level=2'),
       ('fastbuild', '1', 'symbol_level=1'),
       ('fastbuild', '2', 'symbol_level=0'),
       ('OS', 'ios', 'os="ios"'),
       ('OS', 'android', 'os="android"'),
@@ skipping 205 matching lines @@
   if not RunGN(supplemental_includes):
     sys.exit(1)
   args.extend(
       ['-I' + i for i in additional_include_files(supplemental_includes, args)])
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Off we go...
   sys.exit(gyp.main(args))