Format GN files and add a presubmit check that GN is properly formatted

runtime/PRESUBMIT.py

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import os
 import cpplint
 import re
 
 # memcpy does not handle overlapping memory regions. Even though this
 # is well documented it seems to be used in error quite often. To avoid
@@ skipping 26 matching lines @@
       cpplint.ProcessFile(filename, 1)
       # Check for memcpy use.
       memcpy_match_count += CheckMemcpy(filename)
 
   # Report a presubmit error if any of the files had an error.
   if cpplint._cpplint_state.error_count > 0 or memcpy_match_count > 0:
     result = [output_api.PresubmitError('Failed cpplint check.')]
   return result
 
 
+def CheckGn(input_api, output_api):
+  return input_api.canned_checks.CheckGNFormatted(input_api, output_api)
+
+
 def CheckChangeOnUpload(input_api, output_api):
-  return RunLint(input_api, output_api)
+  return (RunLint(input_api, output_api) +
+          CheckGn(input_api, output_api))
 
 
 def CheckChangeOnCommit(input_api, output_api):
-  return RunLint(input_api, output_api)
+  return (RunLint(input_api, output_api) +
+          CheckGn(input_api, output_api))