[test] Let presubmit only run over affected files.

PRESUBMIT.py

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 53 matching lines @@
   """Runs the V8 presubmit checks."""
   import sys
   sys.path.append(input_api.os_path.join(
         input_api.PresubmitLocalPath(), 'tools'))
   from presubmit import CppLintProcessor
   from presubmit import SourceProcessor
   from presubmit import CheckAuthorizedAuthor
   from presubmit import CheckStatusFiles
 
   results = []
-  if not CppLintProcessor().Run(input_api.PresubmitLocalPath()):
+  if not CppLintProcessor().RunOnFiles(input_api.AffectedFiles()):
     results.append(output_api.PresubmitError("C++ lint check failed"))
-  if not SourceProcessor().Run(input_api.PresubmitLocalPath()):
+  if not SourceProcessor().RunOnFiles(input_api.AffectedFiles()):
     results.append(output_api.PresubmitError(
         "Copyright header, trailing whitespaces and two empty lines " \
         "between declarations check failed"))
   if not CheckStatusFiles(input_api.PresubmitLocalPath()):
     results.append(output_api.PresubmitError("Status file check failed"))
   results.extend(CheckAuthorizedAuthor(input_api, output_api))
   return results
 
 
 def _CheckUnwantedDependencies(input_api, output_api):
@@ skipping 195 matching lines @@
 def CheckChangeOnCommit(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   if not _SkipTreeCheck(input_api, output_api):
     results.extend(input_api.canned_checks.CheckTreeIsOpen(
         input_api, output_api,
         json_url='http://v8-status.appspot.com/current?format=json'))
   return results