js_checker.py: Restore smoke tests for linting violations.

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
 
 
 class MockInputApi(object):
   """Mock class for the InputApi class.
 
   This class can be used for unittests for presubmit by initializing the files
   attribute as the list of changed files.
   """
 
   def __init__(self):
     self.json = json
     self.re = re
     self.os_path = os.path
     self.platform = sys.platform
     self.python_executable = sys.executable
     self.platform = sys.platform
     self.subprocess = subprocess
     self.files = []
     self.is_committing = False
     self.change = MockChange([])
+    self.presubmit_local_path = os.path.dirname(__file__)
 
   def AffectedFiles(self, file_filter=None, include_deletes=False):
     return self.files
 
   def AffectedSourceFiles(self, file_filter=None):
     return self.files
 
   def LocalPaths(self):
     return self.files
 
   def PresubmitLocalPath(self):
-    return os.path.dirname(__file__)
+    return self.presubmit_local_path
 
   def ReadFile(self, filename, mode='rU'):
     if hasattr(filename, 'AbsoluteLocalPath'):
        filename = filename.AbsoluteLocalPath()
     for file_ in self.files:
       if file_.LocalPath() == filename:
         return '\n'.join(file_.NewContents())
     # Otherwise, file is not in our mock API.
     raise IOError, "No such file or directory: '%s'" % filename
 
@@ skipping 97 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