Remove remaining unused imports in webkitpy.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock.py

 # Copyright (C) 2009 Google Inc. All rights reserved.
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 # in the documentation and/or other materials provided with the
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 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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-import StringIO
 import errno
 import hashlib
 import os
 import re
+import StringIO
 
 
 class MockFileSystem(object):
     sep = '/'
     pardir = '..'
 
     def __init__(self, files=None, dirs=None, cwd='/'):
         """Initializes a "mock" filesystem that can be used to replace the
         FileSystem class in tests.
 
@@ skipping 451 matching lines @@
         return self.data.readline(length)
 
     def __iter__(self):
         return self.data.__iter__()
 
     def next(self):
         return self.data.next()
 
     def seek(self, offset, whence=os.SEEK_SET):
         self.data.seek(offset, whence)