Add --gerrit_no_reset for who need to use FETCH_HEAD revision.

recipe_modules/bot_update/example.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.
 
 DEPS = [
   'bot_update',
   'gclient',
   'recipe_engine/path',
   'recipe_engine/properties',
 ]
@@ skipping 12 matching lines @@
   patch = api.properties.get('patch', True)
   clobber = True if api.properties.get('clobber') else False
   force = True if api.properties.get('force') else False
   no_shallow = True if api.properties.get('no_shallow') else False
   output_manifest = api.properties.get('output_manifest', False)
   with_branch_heads = api.properties.get('with_branch_heads', False)
   refs = api.properties.get('refs', [])
   oauth2 = api.properties.get('oauth2', False)
   root_solution_revision = api.properties.get('root_solution_revision')
   suffix = api.properties.get('suffix')
+  gerrit_no_reset = True if api.properties.get('gerrit_no_reset') else False
   api.bot_update.ensure_checkout(force=force,
                                  no_shallow=no_shallow,
                                  patch=patch,
                                  with_branch_heads=with_branch_heads,
                                  output_manifest=output_manifest,
                                  refs=refs, patch_oauth2=oauth2,
                                  clobber=clobber,
                                  root_solution_revision=root_solution_revision,
-                                 suffix=suffix)
+                                 suffix=suffix,
+                                 gerrit_no_reset=gerrit_no_reset)
 
 
 def GenTests(api):
   yield api.test('basic') + api.properties(
       mastername='chromium.linux',
       buildername='Linux Builder',
       slavename='totallyaslave-m1',
       patch=False,
       revision='abc'
   )
@@ skipping 84 matching lines @@
       buildername='Experimental Builder',
       slavename='somehost',
       clobber=1
   )
   yield api.test('reset_root_solution_revision') + api.properties(
       mastername='experimental',
       buildername='Experimental Builder',
       slavename='somehost',
       root_solution_revision='revision',
   )
+  yield api.test('gerrit_no_reset') + api.properties(
+      mastername='experimental',
+      buildername='Experimental Builder',
+      slavename='somehost',
+      gerrit_no_reset=1
+  )
   yield api.test('tryjob_v8') + api.properties(
       mastername='tryserver.chromium.linux',
       buildername='linux_rel',
       slavename='totallyaslave-c4',
       issue=12345,
       patchset=654321,
       patch_url='http://src.chromium.org/foo/bar',
       patch_project='v8',
       revisions={'src/v8': 'abc'}
   )