Remove unused imports in webkitpy with using autoflake.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py

 # Copyright (C) 2011 Google Inc. All rights reserved.
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 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
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 # copyright notice, this list of conditions and the following disclaimer
 # in the documentation and/or other materials provided with the
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 # this software without specific prior written permission.
 #
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 import base64
-import copy
 import logging
 import re
 import shlex
 import sys
 import time
-import os
 
 from webkitpy.common.system import path
 from webkitpy.common.system.profiler import ProfilerFactory
 
 
 _log = logging.getLogger(__name__)
 
 
 DRIVER_START_TIMEOUT_SECS = 30
 
@@ skipping 497 matching lines @@
         self.decoded_content = None
         self.malloc = None
         self.js_heap = None
         self.stdin_path = None
 
     def decode_content(self):
         if self.encoding == 'base64' and self.content is not None:
             self.decoded_content = base64.b64decode(self.content)
         else:
             self.decoded_content = self.content