Re-enable GN as part of GYP execution.

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 203 matching lines @@
     gyp_file = os.environ.get('CHROMIUM_GYP_FILE')
     if gyp_file:
       # Note that CHROMIUM_GYP_FILE values can't have backslashes as
       # path separators even on Windows due to the use of shlex.split().
       args.extend(shlex.split(gyp_file))
     else:
       args.append(os.path.join(script_dir, 'all.gyp'))
 
   supplemental_includes = GetSupplementalFiles()
 
-  # Temporarily disabled, http://crbug.com/326146
-  # TODO(brettw) re-enable this code
-  #if not RunGN(supplemental_includes):
-    #sys.exit(1)
+  if not RunGN(supplemental_includes):
+    sys.exit(1)
 
   args.extend(
       ['-I' + i for i in additional_include_files(supplemental_includes, args)])
 
   # There shouldn't be a circular dependency relationship between .gyp files,
   # but in Chromium's .gyp files, on non-Mac platforms, circular relationships
   # currently exist.  The check for circular dependencies is currently
   # bypassed on other platforms, but is left enabled on the Mac, where a
   # violation of the rule causes Xcode to misbehave badly.
   # TODO(mark): Find and kill remaining circular dependencies, and remove this
@@ skipping 46 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))