web_dev_style: actually restore sys.path in various PRESUBMITs

chrome/browser/resources/PRESUBMIT.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.
 
 """Presubmit script for files in chrome/browser/resources.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
@@ skipping 89 matching lines @@
   presubmit_path = input_api.PresubmitLocalPath()
   tests = [input_api.os_path.join(presubmit_path, 'vulcanize_gn_test.py')]
   return input_api.canned_checks.RunUnitTests(input_api, output_api, tests)
 
 
 def _CheckWebDevStyle(input_api, output_api):
   results = []
 
   try:
     import sys
-    old_sys_path = sys.path
+    old_sys_path = sys.path[:]
     cwd = input_api.PresubmitLocalPath()
     sys.path += [input_api.os_path.join(cwd, '..', '..', '..', 'tools')]
     import web_dev_style.presubmit_support
     results += web_dev_style.presubmit_support.CheckStyle(input_api, output_api)
   finally:
     sys.path = old_sys_path
 
   return results
 
 
@@ skipping 16 matching lines @@
   return _CheckChangeOnUploadOrCommit(input_api, output_api)
 
 
 def PostUploadHook(cl, change, output_api):
   return output_api.EnsureCQIncludeTrybotsAreAdded(
     cl,
     [
       'master.tryserver.chromium.linux:closure_compilation',
     ],
     'Automatically added optional Closure bots to run on CQ.')