[polymer] Makes ContainerThatDecoratesItsChildren use HTMLDivElement

tracing/tracing/ui/base/container_that_decorates_its_children.html

Index: tracing/tracing/ui/base/container_that_decorates_its_children.html
diff --git a/tracing/tracing/ui/base/container_that_decorates_its_children.html b/tracing/tracing/ui/base/container_that_decorates_its_children.html
index 227645499e2c1884e61e03b1068c4eaf28ddf37f..0ee972ef03ea0d5dea1da4066b9eef3da08ca4bc 100644
--- a/tracing/tracing/ui/base/container_that_decorates_its_children.html
+++ b/tracing/tracing/ui/base/container_that_decorates_its_children.html
@@ -21,7 +21,7 @@ tr.exportTo('tr.ui.b', function() {
   var ContainerThatDecoratesItsChildren = tr.ui.b.define('div');
 
   ContainerThatDecoratesItsChildren.prototype = {
-    __proto__: HTMLUnknownElement.prototype,
+    __proto__: HTMLDivElement.prototype,
 
     decorate: function() {
       this.observer_ = new WebKitMutationObserver(this.didMutate_.bind(this));
@@ -34,24 +34,23 @@ tr.exportTo('tr.ui.b', function() {
           { get: undefined, set: this.onSetTextContent_});
     },
 
-    // TODO(polymer): Do we need to use Polymer.dom on these functions?
     appendChild: function(x) {
-      Polymer.dom(HTMLUnknownElement.prototype).appendChild.call(this, x);

[charliea (OOO until 10-5), 2016/04/28 18:02:15]

I don't think that we need to wrap this in Polymer.dom because `this` should
have already been Polymer.dom'ed by this point.

[aiolos (Not reviewing), 2016/04/28 18:03:42]

That seems likely

+      HTMLDivElement.prototype.appendChild.call(this, x);
       this.didMutate_(this.observer_.takeRecords());
     },
 
     insertBefore: function(x, y) {
-      HTMLUnknownElement.prototype.insertBefore.call(this, x, y);
+      HTMLDivElement.prototype.insertBefore.call(this, x, y);
       this.didMutate_(this.observer_.takeRecords());
     },
 
     removeChild: function(x) {
-      HTMLUnknownElement.prototype.removeChild.call(this, x);
+      HTMLDivElement.prototype.removeChild.call(this, x);
       this.didMutate_(this.observer_.takeRecords());
     },
 
     replaceChild: function(x, y) {
-      HTMLUnknownElement.prototype.replaceChild.call(this, x, y);
+      HTMLDivElement.prototype.replaceChild.call(this, x, y);
       this.didMutate_(this.observer_.takeRecords());
     },
 
@@ -63,7 +62,7 @@ tr.exportTo('tr.ui.b', function() {
 
     clear: function() {
       while (this.lastChild)
-        HTMLUnknownElement.prototype.removeChild.call(this, this.lastChild);
+        HTMLDivElement.prototype.removeChild.call(this, this.lastChild);
       this.didMutate_(this.observer_.takeRecords());
     },