Expose the chromium waterfall in sheriff-o-matic.

Tools/GardeningServer/ui/ct-test-list.html

Index: Tools/GardeningServer/ui/ct-test-list.html
diff --git a/Tools/GardeningServer/ui/ct-test-list.html b/Tools/GardeningServer/ui/ct-test-list.html
index 1f87d99d1063d18b19b7da24d296c651471e9345..dde33b6f643a6467d5dc354695b15ba53099178f 100644
--- a/Tools/GardeningServer/ui/ct-test-list.html
+++ b/Tools/GardeningServer/ui/ct-test-list.html
@@ -4,7 +4,7 @@ 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 {
@@ -19,7 +19,7 @@ found in the LICENSE file.
   <script>
     Polymer({
       flakinessDashboardURL: function(test) {
-        return ui.urlForFlakinessDashboard(test.testName, test.step);
+        return ui.urlForFlakinessDashboard(test.testName, test.step, this.tree);
       },
     });
   </script>