LayoutTree machinery

tracing/tracing/extras/chrome/layout_tree.html

Index: tracing/tracing/extras/chrome/layout_tree.html
diff --git a/tracing/tracing/extras/chrome/layout_tree.html b/tracing/tracing/extras/chrome/layout_tree.html
index 98e8f14e09925e20e9ba4ab7943bf4b677bc7b92..bf57f69fcaa3ef9b69d337b138eb903bd09f10a0 100644
--- a/tracing/tracing/extras/chrome/layout_tree.html
+++ b/tracing/tracing/extras/chrome/layout_tree.html
@@ -5,6 +5,7 @@ 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/extras/chrome/layout_object.html">
 <link rel="import" href="/tracing/model/event_registry.html">
 <link rel="import" href="/tracing/model/object_instance.html">
 
@@ -27,11 +28,48 @@ tr.exportTo('tr.e.chrome', function() {
 
   function LayoutTreeSnapshot() {
     ObjectSnapshot.apply(this, arguments);
-    this.rootLayoutObject = new tr.e.chrome.LayoutObject(this, this.args);
+
+    // If this LayoutTree is a subframe like an iframe, then this is the
+    // LayoutObject that contains it:
+    this.parentLayoutObject_ = undefined;
+
+    // The LocalFrame should be 1:1 with a RenderFrame object, which should be
+    // 1:1 with a FrameTreeNode object.
   }
 
   LayoutTreeSnapshot.prototype = {
     __proto__: ObjectSnapshot.prototype,
+
+    initialize: function() {
+      this.rootLayoutObject = new tr.e.chrome.LayoutObject(this, this.args);
+    },
+
+    get parentLayoutObject() {
+      return this.parentLayoutObject_;
+    },
+
+    get parentLayoutTreeSnapshot() {
+      if (this.parentLayoutObject)
+        return this.parentLayoutObject.snapshot;
+      return undefined;
+    },
+
+    get rootLayoutTreeSnapshot() {
+      var o = this;
+      while (o.parentLayoutObject && o.parentLayoutObject.snapshot) {
+        o = o.parentLayoutObject.snapshot;
+      }
+      return o;
+    },
+
+    set parentLayoutObject(o) {
+      if (this.parentLayoutObject_) {
+        console.warn('Duplicate parentLayoutObject: ' +
+                     'TODO split LayoutTreeSnapshot ',
+                     this.parentLayoutObject, o);
+      }
+      this.parentLayoutObject_ = o;
+    }
   };
 
   ObjectSnapshot.register(LayoutTreeSnapshot, {typeName: 'LayoutTree'});