Make use of dry_run property of presubmit tryjobs.

scripts/slave/recipes/run_presubmit.py

 # Copyright (c) 2013 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 = [
   'depot_tools/bot_update',
   'depot_tools/gclient',
   'depot_tools/git',
   'depot_tools/presubmit',
   'recipe_engine/json',
@@ skipping 60 matching lines @@
     # Field event.patchSet.ref looks like 'refs/changes/11/338811/4'
     issue, patchset = api.properties['event.patchSet.ref'].split('/')[-2:]
     presubmit_args = [
       '--issue', issue,
       '--patchset', patchset,
       '--gerrit_url', api.properties['gerrit'],
       '--gerrit_fetch',
     ]
   else:  # pragma: no cover
     assert False, 'patch_storage %s is not supported' % patch_storage
+  if api.properties.get('dry_run'):
+    presubmit_args.append('--dry_run')
 
   presubmit_args.extend([
     '--root', abs_root,
     '--commit',
     '--verbose', '--verbose',
     '--skip_canned', 'CheckRietveldTryJobExecution',
     '--skip_canned', 'CheckTreeIsOpen',
     '--skip_canned', 'CheckBuildbotPendingBuilds',
     '--upstream', upstream,  # '' if not in bot_update mode.
   ])
@@ skipping 37 matching lines @@
     api.properties.tryserver(
         mastername='experimental.svn',
         buildername='chromium_presubmit',
         repo_name='chromium',
         force_checkout=True) +
     api.step_data('presubmit', api.json.output([['chromium_presubmit',
                                                  ['compile']]]))
   )
 
   yield (
+    api.test('chromium_dry_run') +
+    api.properties.tryserver(
+        mastername='tryserver.chromium.linux',
+        buildername='chromium_presubmit',
+        repo_name='chromium',
+        patch_project='chromium',
+        dry_run=True) +
+    api.step_data('presubmit', api.json.output([['chromium_presubmit',
+                                                 ['compile']]]))
+  )
+
+  yield (
     api.test('chromium_with_auth') +
     api.properties.tryserver(
         mastername='tryserver.chromium.linux',
         buildername='chromium_presubmit',
         repo_name='chromium',
         codereview_auth=True,
         patch_project='chromium') +
     api.step_data('presubmit', api.json.output([['chromium_presubmit',
                                                  ['compile']]]))
   )
@@ skipping 26 matching lines @@
     api.test('recipes-py') +
     api.properties.tryserver(
         mastername='tryserver.infra',
         buildername='infra_presubmit',
         repo_name='recipes_py',
         patch_project='recipes-py',
         runhooks=True) +
     api.step_data('presubmit', api.json.output([['infra_presubmit',
                                                  ['compile']]]))
   )