Adding PRESUBMIT check on google::protobuf

PRESUBMIT.py

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import json
 import os
@@ skipping 455 matching lines @@
   for directory in test_directories:
     tests.extend(
       input_api.canned_checks.GetUnitTestsInDirectory(
           input_api,
           output_api,
           directory,
           whitelist=[r'.+_test\.py$']))
   return input_api.RunTests(tests, parallel=True)
 
 
+def _CheckUsageOfGoogleProtobufNamespace(input_api, output_api):
+  """Checks that the namespace google::protobuf has not been used."""
+  files = []
+  pattern = input_api.re.compile(r'google::protobuf')
+  proto_utils_path = os.path.join('webrtc', 'base', 'protobuf_utils.h')
+  for f in input_api.AffectedSourceFiles(input_api.FilterSourceFile):
+    if f.LocalPath() in [proto_utils_path, 'PRESUBMIT.py']:
+      continue
+    contents = input_api.ReadFile(f)
+    if pattern.search(contents):
+      files.append(f)
+
+  if files:
+    return [output_api.PresubmitError(
+        'Please avoid to use namespace `google::protobuf` directly.\n'
+        'Add a using directive in `%s` and include that header instead.'
+        % proto_utils_path, files)]
+  return []
+
+
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
   # Filter out files that are in objc or ios dirs from being cpplint-ed since
   # they do not follow C++ lint rules.
   black_list = input_api.DEFAULT_BLACK_LIST + (
     r".*\bobjc[\\\/].*",
     r".*objc\.[hcm]+$",
     r"webrtc\/build\/ios\/SDK\/.*",
   )
@@ skipping 48 matching lines @@
   results.extend(input_api.canned_checks.CheckChangeTodoHasOwner(
       input_api, output_api))
   results.extend(_CheckNativeApiHeaderChanges(input_api, output_api))
   results.extend(_CheckNoIOStreamInHeaders(input_api, output_api))
   results.extend(_CheckNoPragmaOnce(input_api, output_api))
   results.extend(_CheckNoFRIEND_TEST(input_api, output_api))
   results.extend(_CheckGnChanges(input_api, output_api))
   results.extend(_CheckUnwantedDependencies(input_api, output_api))
   results.extend(_CheckJSONParseErrors(input_api, output_api))
   results.extend(_RunPythonTests(input_api, output_api))
+  results.extend(_CheckUsageOfGoogleProtobufNamespace(input_api, output_api))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(
       input_api.canned_checks.CheckGNFormatted(input_api, output_api))
   return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(_VerifyNativeApiHeadersListIsValid(input_api, output_api))
   results.extend(input_api.canned_checks.CheckOwners(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeWasUploaded(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   results.extend(_CheckChangeHasBugField(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasTestField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api, output_api,
       json_url='http://webrtc-status.appspot.com/current?format=json'))
   return results