Remove uses of #pragma once and add PRESUBMIT check.

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 151 matching lines @@
 
   if len(files):
     return [output_api.PresubmitError(
         'Do not #include <iostream> in header files, since it inserts static ' +
         'initialization into every file including the header. Instead, ' +
         '#include <ostream>. See http://crbug.com/94794',
         files)]
   return []
 
 
+def _CheckNoPragmaOnce(input_api, output_api):
+  """Make sure that banned functions are not used."""
+  files = []
+  pattern = input_api.re.compile(r'^#pragma\s+once',
+                                 input_api.re.MULTILINE)
+  for f in input_api.AffectedSourceFiles(input_api.FilterSourceFile):
+    if not f.LocalPath().endswith('.h'):
+      continue
+    contents = input_api.ReadFile(f)
+    if pattern.search(contents):
+      files.append(f)
+
+  if files:
+    return [output_api.PresubmitError(
+        'Do not use #pragma once in header files.\n'
+        'See http://www.chromium.org/developers/coding-style#TOC-File-headers',
+        files)]
+  return []
+
+
 def _CheckNoFRIEND_TEST(input_api, output_api):
   """Make sure that gtest's FRIEND_TEST() macro is not used, the
   FRIEND_TEST_ALL_PREFIXES() macro from testsupport/gtest_prod_util.h should be
   used instead since that allows for FLAKY_, FAILS_ and DISABLED_ prefixes."""
   problems = []
 
   file_filter = lambda f: f.LocalPath().endswith(('.cc', '.h'))
   for f in input_api.AffectedFiles(file_filter=file_filter):
     for line_num, line in f.ChangedContents():
       if 'FRIEND_TEST(' in line:
@@ skipping 325 matching lines @@
   results.extend(input_api.canned_checks.CheckChangeHasNoTabs(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasNoStrayWhitespace(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckAuthorizedAuthor(
       input_api, output_api))
   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))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
@@ skipping 12 matching lines @@
       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