[polymer] Switches .appendChild() to Polymer.dom()...appendChild()

tracing/tracing/ui/tracks/drawing_container_perf_test.html

Index: tracing/tracing/ui/tracks/drawing_container_perf_test.html
diff --git a/tracing/tracing/ui/tracks/drawing_container_perf_test.html b/tracing/tracing/ui/tracks/drawing_container_perf_test.html
index 41f9aa87fff032dec47809f571f397daffc22f83..bd0ffe0aeff8cee35feeb4ddd4512ee7d234788b 100644
--- a/tracing/tracing/ui/tracks/drawing_container_perf_test.html
+++ b/tracing/tracing/ui/tracks/drawing_container_perf_test.html
@@ -42,11 +42,11 @@ tr.b.unittest.testSuite(function() {
       this.viewport.modelTrackContainer = this.drawingContainer;
 
       var modelTrack = new tr.ui.tracks.ModelTrack(this.viewport);
-      this.drawingContainer.appendChild(modelTrack);
+      Polymer.dom(this.drawingContainer).appendChild(modelTrack);
 
       modelTrack.model = model;
 
-      this.viewportDiv.appendChild(this.drawingContainer);
+      Polymer.dom(this.viewportDiv).appendChild(this.drawingContainer);
 
       this.addHTMLOutput(this.viewportDiv);