Presubmit: Warn about useless forward declarations

PRESUBMIT_test_mocks.py

 # Copyright 2014 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.
 
 import json
 import os
 import re
 import subprocess
 import sys
 
@@ skipping 81 matching lines @@
 
   This class can be used to form the mock list of changed files in
   MockInputApi for presubmit unittests.
   """
 
   def __init__(self, local_path, new_contents, action='A'):
     self._local_path = local_path
     self._new_contents = new_contents
     self._changed_contents = [(i + 1, l) for i, l in enumerate(new_contents)]
     self._action = action
+    self._scm_diff = "--- /dev/null\n+++ %s\n@@ -0,0 +1,%d @@\n" % (local_path,
+      len(new_contents))
+    for l in new_contents:
+      self._scm_diff += "+%s\n" % l
 
   def Action(self):
     return self._action
 
   def ChangedContents(self):
     return self._changed_contents
 
   def NewContents(self):
     return self._new_contents
 
   def LocalPath(self):
     return self._local_path
 
   def AbsoluteLocalPath(self):
     return self._local_path
 
+  def GenerateScmDiff(self):
+    return self._scm_diff;
+
   def rfind(self, p):
     """os.path.basename is called on MockFile so we need an rfind method."""
     return self._local_path.rfind(p)
 
   def __getitem__(self, i):
     """os.path.basename is called on MockFile so we need a get method."""
     return self._local_path[i]
 
   def __len__(self):
     """os.path.basename is called on MockFile so we need a len method."""
@@ skipping 14 matching lines @@
 
   def __init__(self, changed_files):
     self._changed_files = changed_files
 
   def LocalPaths(self):
     return self._changed_files
 
   def AffectedFiles(self, include_dirs=False, include_deletes=True,
                     file_filter=None):
     return self._changed_files