[Sheriff-o-matic] Remove race condition on the commit list.

Tools/GardeningServer/model/ct-commit-list-mock.html

+<!--
+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.
+-->
+
+<link rel='import' href='ct-commit-list.html'>
+
+<link rel='import' href='ct-commit-log-mock.html'>
+
+<script>
+(function () {
+
+window.CTCommitListMock = function() {
+  var group = {
+    failures: [
+      {
+        firstFailingRevisions: {
+          'blink': 158545
+        },
+        lastPassingRevisions: {
+          'blink': 158544
+        }
+      }
+    ]
+  };
+  return new CTCommitList(group, new CTCommitLogMock());
+};
+
+})();
+</script>