Improve error handling for js2gtest C++ generation.

tools/gypv8sh.py

 #!/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 used by chrome_tests.gypi's js2webui action to maintain the
 argument lists and to generate inlinable tests.
 """
 
 import json
@@ skipping 47 matching lines @@
                cxxoutfile, test_type]
   cmd.extend(['-e', "arguments=" + json.dumps(arguments), mock_js,
          test_api, js2webui])
   if opts.verbose or opts.impotent:
     print cmd
   if not opts.impotent:
     try:
       p = subprocess.Popen(
           cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, bufsize=0)
       out, err = p.communicate()
+      if p.returncode != 0:
+        sys.stderr.write(out + err);
+        return 1
       if not HasSameContent(cxxoutfile, out):
         with open(cxxoutfile, 'wb') as f:
           f.write(out)
       shutil.copyfile(inputfile, jsoutfile)
     except Exception, ex:
       if os.path.exists(cxxoutfile):
         os.remove(cxxoutfile)
       if os.path.exists(jsoutfile):
         os.remove(jsoutfile)
       raise
 
 
 if __name__ == '__main__':
   sys.exit(main())