Move commit list out its own model.

Tools/GardeningServer/ui/ct-failure-card.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-builder-grid.html">
 <link rel="import" href="ct-commit-list.html">
 <link rel="import" href="ct-test-list.html">
 
@@ skipping 47 matching lines @@
         flex-direction: column;
       }
 
       .snoozed {
         opacity: 0.5;
       }
     </style>
     <ct-builder-grid failures="{{ group.failures }}"></ct-builder-grid>
     <div id="failure" class="{{ { snoozed: group.isSnoozed } | tokenList }}">
       <ct-test-list tests="{{ group.failures }}" tree="{{ tree }}"></ct-test-list>
-      <ct-commit-list first="{{ group.failures[0].lastPassingRevisions }}"
-          last="{{ group.failures[0].firstFailingRevisions }}"
-          commits="{{ commits }}"></ct-commit-list>
+      <ct-commit-list commitList="{{ _commits() }}"></ct-commit-list>
     </div>
     <div id="buttons">
       <paper-button id="examine" on-tap="{{ examine }}" label="Examine"></paper-button>
       <template if="{{ !group.isSnoozed }}">
         <paper-button id="snooze" on-tap="{{ snooze }}" label="Snooze"></paper-button>
       </template>
       <template if="{{ group.isSnoozed }}">
         <paper-button id="snooze" on-tap="{{ unsnooze }}" label="Unsnooze"></paper-button>
       </template>
     </div>
   </template>
   <script>
     Polymer({
       group: null,
-      commits: {},
+      commits: null,
       tree: '',
 
       examine: function() {
         this.fire('ct-examine-failures', this.group);
       },
 
       snooze: function() {
         this.group.snoozeUntil(Date.now() + 60 * 60 * 1000);
       },
 
       unsnooze: function() {
         this.group.unsnooze();
       },
+
+      _commits: function() {
+        if (!this.group)
+          return undefined;
+        return this.group.commitList(this.commits);
+      }
     });
   </script>
 </polymer-element>