Do not actually remove trees when test bisect in dry-run mode

tools/auto_bisect/bisect_perf_regression_test.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 os
 import re
+import shutil
 import unittest
 
 import bisect_perf_regression
 import source_control as source_control_module
 
 def _GetBisectPerformanceMetricsInstance():
   """Returns an instance of the BisectPerformanceMetrics class."""
   options_dict = {
     'debug_ignore_build': True,
     'debug_ignore_sync': True,
@@ skipping 223 matching lines @@
         276628, 'chromium')
 
   # This method doesn't reference self; it fails if an error is thrown.
   # pylint: disable=R0201
   def testDryRun(self):
     """Does a dry run of the bisect script.
 
     This serves as a smoke test to catch errors in the basic execution of the
     script.
     """
-    bisect_instance = _GetBisectPerformanceMetricsInstance()
-    results = bisect_instance.Run(bisect_instance.opts.command,
-                                  bisect_instance.opts.bad_revision,
-                                  bisect_instance.opts.good_revision,
-                                  bisect_instance.opts.metric)
-    bisect_instance.FormatAndPrintResults(results)
+    # Disable rmtree to avoid deleting local trees.
+    old_rmtree = shutil.rmtree
+    try:
+      shutil.rmtree = lambda path, onerror: None
+      bisect_instance = _GetBisectPerformanceMetricsInstance()
+      results = bisect_instance.Run(bisect_instance.opts.command,
+                                    bisect_instance.opts.bad_revision,
+                                    bisect_instance.opts.good_revision,
+                                    bisect_instance.opts.metric)
+      bisect_instance.FormatAndPrintResults(results)
+    finally:
+      shutil.rmtree = old_rmtree
 
   def testGetCommitPosition(self):
     bisect_instance = _GetBisectPerformanceMetricsInstance()
     cp_git_rev = '7017a81991de983e12ab50dfc071c70e06979531'
     self.assertEqual(
         291765, bisect_instance.source_control.GetCommitPosition(cp_git_rev))
 
     svn_git_rev = 'e6db23a037cad47299a94b155b95eebd1ee61a58'
     self.assertEqual(
         291467, bisect_instance.source_control.GetCommitPosition(svn_git_rev))
@@ skipping 28 matching lines @@
     git_revision = 'a12345789a23456789a123456789a123456789'
     updated_content = bisect_instance.UpdateDepsContents(
         deps_contents, depot, git_revision, deps_key)
     self.assertIsNotNone(updated_content)
     ss = re.compile('["\']%s["\']: ["\']%s["\']' % (deps_key, git_revision))
     self.assertIsNotNone(re.search(ss, updated_content))
 
 
 if __name__ == '__main__':
   unittest.main()