Convert clang=1 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 103 matching lines @@
 
   vars_dict = GetGypVarsForGN(supplemental_files)
   gn_args = ''
 
   # 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 = [
       ('branding', 'Chrome', 'is_chrome_branded=true'),
       ('buildtype', 'Official', 'is_official_build=true'),
       ('component', 'shared_library', 'is_component_build=true'),
+      ('clang', '1', 'is_clang=true'),
   ]
   for i in remap_cases:
     if i[0] in vars_dict and vars_dict[i[0]] == i[1]:
       gn_args += ' ' + i[2]
 
   # These string arguments get passed directly.
   for v in ['windows_sdk_path']:
     if v in vars_dict:
       gn_args += ' ' + v + '=' + EscapeStringForGN(vars_dict[v])
 
@@ skipping 178 matching lines @@
   # to enfore syntax checking.
   syntax_check = os.environ.get('CHROMIUM_GYP_SYNTAX_CHECK')
   if syntax_check and int(syntax_check):
     args.append('--check')
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Off we go...
   sys.exit(gyp.main(args))