Use underscores to separate words in filenames in webkitpy.

third_party/WebKit/Tools/Scripts/webkitpy/formatter/main_unittest.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 StringIO
 import unittest
 
-from webkitpy.common.system.systemhost_mock import MockSystemHost
+from webkitpy.common.system.system_host_mock import MockSystemHost
 from webkitpy.formatter.main import main
 
 
 ACTUAL_INPUT = '''
 def foo():
     """triple-quoted docstring"""
     try:
         bar = "bar"
         long_list = ['this is a list of strings that should be wrapped', "and consistently quoted"]
         longer_list = ['this is a list of strings that should be wrapped', "and consistently quoted", "because it's important to test quoting"]
@@ skipping 124 matching lines @@
 
      """
 ''')
         main(host, ['-'])
         self.assertMultiLineEqual(host.stdout.getvalue(), '''
 def f():
     """This is a docstring
        With extra indentation on this line.
     """
 ''')