Keep two empty lines between declarations for cpp 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 26 matching lines @@
   sys.path.append(input_api.os_path.join(
         input_api.PresubmitLocalPath(), 'tools'))
   from presubmit import CppLintProcessor
   from presubmit import SourceProcessor
 
   results = []
   if not CppLintProcessor().Run(input_api.PresubmitLocalPath()):
     results.append(output_api.PresubmitError("C++ lint check failed"))
   if not SourceProcessor().Run(input_api.PresubmitLocalPath()):
     results.append(output_api.PresubmitError(
-        "Copyright header and trailing whitespaces check failed"))
+        "Copyright header, trailing whitespaces and two empty lines " \
+        "between declarations check failed"))
   return results
 
 
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
   results.extend(input_api.canned_checks.CheckOwners(
       input_api, output_api, source_file_filter=None))
   results.extend(_V8PresubmitChecks(input_api, output_api))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   return results
 
 
 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))
   return results