[polymer] Replaces this.appendChild with Polymer.dom(this).appendChild

tracing/tracing/ui/extras/chrome/cc/layer_picker.html

Index: tracing/tracing/ui/extras/chrome/cc/layer_picker.html
diff --git a/tracing/tracing/ui/extras/chrome/cc/layer_picker.html b/tracing/tracing/ui/extras/chrome/cc/layer_picker.html
index 780fe03d86c49a823e46e9eace02b20dba7b3055..d76ad649ac2d1ddef6970b46cd64751d94364f9b 100644
--- a/tracing/tracing/ui/extras/chrome/cc/layer_picker.html
+++ b/tracing/tracing/ui/extras/chrome/cc/layer_picker.html
@@ -41,9 +41,9 @@ tr.exportTo('tr.ui.e.chrome.cc', function() {
 
 
       this.itemList_ = new tr.ui.b.ListView();
-      this.appendChild(this.controls_);
+      Polymer.dom(this).appendChild(this.controls_);
 
-      this.appendChild(this.itemList_);
+      Polymer.dom(this).appendChild(this.itemList_);
 
       this.itemList_.addEventListener(
           'selection-changed', this.onItemSelectionChanged_.bind(this));