CQ: do not force HEAD revision for chromium_trybot builders

This will make it possible to use LKCR.

BUG=317931

Review URL: https://codereview.chromium.org/141233003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/commit-queue@247481 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/projects.py b/projects.py
index 8ca0b72..df33c3f 100644
--- a/projects.py
+++ b/projects.py
@@ -459,11 +459,15 @@
 
     # Experimental recipe-based Chromium trybots. To avoid possible capacity
     # problems, only enable for a small percentage of try runs.
-    # Disable as emergency measure - crbug.com/334681
+    #
+    # Note how we pass revision=None . In presence of safesync_url
+    # this makes a difference: no revision uses safesync_url,
+    # while HEAD ignores it and always fetches latest revision.
     verifiers.append(
         trigger_experimental_try_job.TriggerExperimentalTryJobVerifier(
             context_obj,
             percentage=0.25,
+            revision=None,
             try_job_description={
                 'linux_chromium_rel': ['defaulttests'],
                 'mac_chromium_rel': ['defaulttests'],
diff --git a/verification/trigger_experimental_try_job.py b/verification/trigger_experimental_try_job.py
index 0e8b144..26ee561 100644
--- a/verification/trigger_experimental_try_job.py
+++ b/verification/trigger_experimental_try_job.py
@@ -13,17 +13,18 @@
 class TriggerExperimentalTryJobVerifier(base.Verifier):
   name = 'trigger experimental try job'
 
-  def __init__(self, context, percentage, try_job_description):
+  def __init__(self, context, percentage, revision, try_job_description):
     super(TriggerExperimentalTryJobVerifier, self).__init__()
     self.context = context
     self.percentage = percentage
+    self.revision = revision
     self.try_job_description = try_job_description
 
   def verify(self, pending):
     if random.random() < self.percentage:
       try:
         self.context.rietveld.trigger_try_jobs(
-            pending.issue, pending.patchset, 'CQ', False, 'HEAD',
+            pending.issue, pending.patchset, 'CQ', False, self.revision,
             self.try_job_description)
       except urllib2.HTTPError as e:
         if e.code not in (400, 500, 503):