Added virtualenv for depot_tools

PRESUBMIT.py

 # Copyright (c) 2012 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.
 
 """Top-level presubmit script for depot tools.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API built into depot_tools.
 """
 
 import fnmatch
 import os
 
 
 def CommonChecks(input_api, output_api, tests_to_black_list):
   results = []
   results.extend(input_api.canned_checks.CheckOwners(input_api, output_api))
   black_list = list(input_api.DEFAULT_BLACK_LIST) + [
       r'^cpplint\.py$',
       r'^cpplint_chromium\.py$',
       r'^external_bin[\/\\].+',
       r'^python[0-9]*_bin[\/\\].+',
       r'^site-packages-py[0-9]\.[0-9][\/\\].+',
       r'^svn_bin[\/\\].+',
-      r'^testing_support[\/\\]_rietveld[\/\\].+']
+      r'^testing_support[\/\\]_rietveld[\/\\].+',
+      r'^bootstrap[\/\\].+']
   if os.path.exists('.gitignore'):
     with open('.gitignore') as fh:
       lines = [l.strip() for l in fh.readlines()]
       black_list.extend([fnmatch.translate(l) for l in lines if
                          l and not l.startswith('#')])
   if os.path.exists('.git/info/exclude'):
     with open('.git/info/exclude') as fh:
       lines = [l.strip() for l in fh.readlines()]
       black_list.extend([fnmatch.translate(l) for l in lines if
                          l and not l.startswith('#')])
@@ skipping 85 matching lines @@
 
 
 def CheckChangeOnCommit(input_api, output_api):
   output = []
   output.extend(CommonChecks(input_api, output_api, []))
   output.extend(input_api.canned_checks.CheckDoNotSubmit(
       input_api,
       output_api))
   output.extend(RunGitClTests(input_api, output_api))
   return output