Expose the chromium waterfall in sheriff-o-matic.

Tools/GardeningServer/ui/ct-test-list.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.
 -->
 
-<polymer-element name="ct-test-list" attributes="tests">
+<polymer-element name="ct-test-list" attributes="tests tree">
   <template>
     <style>
       :host {
         display: block;
       }
     </style>
     <template repeat="{{ test in tests }}">
       <!-- FIXME: Find a less redundant UI than repeating the step on each line. -->
       <div>{{ test.step }} <a href="{{ test | flakinessDashboardURL }}">{{ test.testName }}</a></div>
     </template>
   </template>
   <script>
     Polymer({
       flakinessDashboardURL: function(test) {
-        return ui.urlForFlakinessDashboard(test.testName, test.step);
+        return ui.urlForFlakinessDashboard(test.testName, test.step, this.tree);
       },
     });
   </script>
 </polymer-element>