Presubmit: Skip third_party for fwd decl warning

PRESUBMIT.py

 # 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
@@ skipping 1568 matching lines @@
 
   if len(files):
     return [output_api.PresubmitError(
         'Do not introduce new mojom targets with use_new_wrapper_types set to '
         'false. The mode is deprecated and will be removed soon.',
         files)]
   return []
 
 
 def _CheckUselessForwardDeclarations(input_api, output_api):
-  """Checks that added or removed lines in affected header files
-     do not lead to new useless class or struct forward declaration.
+  """Checks that added or removed lines in non third party affected
+     header files do not lead to new useless class or struct forward
+     declaration.
   """
   results = []
   class_pattern = input_api.re.compile(r'^class\s+(\w+);$',
                                        input_api.re.MULTILINE)
   struct_pattern = input_api.re.compile(r'^struct\s+(\w+);$',
                                         input_api.re.MULTILINE)
   for f in input_api.AffectedFiles(include_deletes=False):
+    if (f.LocalPath().startswith('third_party') and
+        not f.LocalPath().startswith('third_party/WebKit') and
+        not f.LocalPath().startswith('third_party\\WebKit')):
+      continue
+
     if not f.LocalPath().endswith('.h'):
       continue
 
     contents = input_api.ReadFile(f)
     fwd_decls = input_api.re.findall(class_pattern, contents)
     fwd_decls.extend(input_api.re.findall(struct_pattern, contents))
 
     useless_fwd_decls = []
     for decl in fwd_decls:
       count = sum(1 for _ in input_api.re.finditer(
@@ skipping 714 matching lines @@
   results.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api,
       output_api,
       json_url='http://chromium-status.appspot.com/current?format=json'))
 
   results.extend(input_api.canned_checks.CheckChangeHasBugField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   return results