Expose the chromium waterfall in sheriff-o-matic.

Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.html

Index: Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.html
diff --git a/Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.html b/Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.html
index 949ed4bada2c3411047e0423deeb346442e2e806..393b55c97822911753623a515cac8d672cfb59ef 100644
--- a/Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.html
+++ b/Tools/GardeningServer/ui/ct-embedded-flakiness-dashboard.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-embedded-flakiness-dashboard" attributes="test">
+<polymer-element name="ct-embedded-flakiness-dashboard" attributes="test tree">
   <template>
     <style>
       :host {
@@ -20,6 +20,7 @@ found in the LICENSE file.
   <script>
     Polymer({
       test: "",
+      tree: "",
 
       ready: function() {
         window.addEventListener('message', function(event) {
@@ -31,7 +32,7 @@ found in the LICENSE file.
       },
 
       testChanged: function() {
-        this.$.iframe.src = ui.urlForEmbeddedFlakinessDashboard(this.test.testName, this.test.step);
+        this.$.iframe.src = ui.urlForEmbeddedFlakinessDashboard(this.test.testName, this.test.step, this.tree);
       },
 
     });