Introduce base classes for blame contexts

tracing/tracing/extras/chrome/blame_context/render_frame.html

Index: tracing/tracing/extras/chrome/blame_context/render_frame.html
diff --git a/tracing/tracing/extras/chrome/render_frame.html b/tracing/tracing/extras/chrome/blame_context/render_frame.html
similarity index 49%
rename from tracing/tracing/extras/chrome/render_frame.html
rename to tracing/tracing/extras/chrome/blame_context/render_frame.html
index 8703e55d74147d3568e1c844698a9ee254b7d0b3..3bd29e907fe734b770dc7275f8fb286e50aff8a2 100644
--- a/tracing/tracing/extras/chrome/render_frame.html
+++ b/tracing/tracing/extras/chrome/blame_context/render_frame.html
@@ -5,56 +5,69 @@ Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
-<link rel="import" href="/tracing/model/object_instance.html">
+<link rel="import" href="/tracing/extras/chrome/blame_context/blame_context.html">
 
 <script>
 'use strict';
 
+/**
+ * @fileoverview Trace Viewer side's correspondence of Chrome's
+ * content::FrameBlameContext class.
+ *
+ */
 tr.exportTo('tr.e.chrome', function() {
-  var constants = tr.e.cc.constants;
-
-  var ObjectSnapshot = tr.model.ObjectSnapshot;
-  var ObjectInstance = tr.model.ObjectInstance;
+  var BlameContextSnapshot = tr.e.chrome.BlameContextSnapshot;
+  var BlameContextInstance = tr.e.chrome.BlameContextInstance;
 
   function RenderFrameSnapshot() {
-    ObjectSnapshot.apply(this, arguments);
+    BlameContextSnapshot.apply(this, arguments);
   }
 
   RenderFrameSnapshot.prototype = {
-    __proto__: ObjectSnapshot.prototype,
-
-    preInitialize: function() {
-    },
-
-    initialize: function() {
-    },
+    __proto__: BlameContextSnapshot.prototype,
 
     referencedAt: function(item, object, field) {
       if (item instanceof tr.e.chrome.FrameTreeNodeSnapshot &&
           object === item.args &&
-          field === 'RenderFrame') {
+          field === 'renderFrame') {
         this.args.frameTreeNode = item;
       }
     },
 
+    get frameTreeNode() {
+      if (this.args.frameTreeNode instanceof tr.e.chrome.FrameTreeNodeSnapshot)
+        return this.args.frameTreeNode;
+      return undefined;
+    },
+
+    get url() {
+      if (this.frameTreeNode)
+        return this.frameTreeNode.url;
+      return undefined;
+    },
+
     get userFriendlyName() {
       return 'RenderFrame';
     }
   };
 
-  ObjectSnapshot.register(
+  tr.model.ObjectSnapshot.register(
       RenderFrameSnapshot,
       {typeName: 'RenderFrame'});
 
   function RenderFrameInstance() {
-    ObjectInstance.apply(this, arguments);
+    BlameContextInstance.apply(this, arguments);
   }
 
   RenderFrameInstance.prototype = {
-    __proto__: ObjectInstance.prototype
+    __proto__: BlameContextInstance.prototype,
+
+    get blameContextType() {
+      return 'Frame';
+    }
   };
 
-  ObjectInstance.register(
+  tr.model.ObjectInstance.register(
       RenderFrameInstance,
       {typeName: 'RenderFrame'});