Use Polymer.dom with many dom manipulations.

tracing/tracing/ui/tracks/model_track.html

Index: tracing/tracing/ui/tracks/model_track.html
diff --git a/tracing/tracing/ui/tracks/model_track.html b/tracing/tracing/ui/tracks/model_track.html
index ff5f12dcb7fbeae11080fe493a24d5ddb9de66e9..fa05bd5906e86244f85ce7fb6955319641ecedf6 100644
--- a/tracing/tracing/ui/tracks/model_track.html
+++ b/tracing/tracing/ui/tracks/model_track.html
@@ -42,7 +42,7 @@ tr.exportTo('tr.ui.tracks', function() {
 
     decorate: function(viewport) {
       tr.ui.tracks.ContainerTrack.prototype.decorate.call(this, viewport);
-      this.classList.add('model-track');
+      Polymer.dom(this).classList.add('model-track');
 
       var typeInfos = tr.ui.tracks.Highlighter.getAllRegisteredTypeInfos();
       this.highlighters_ = typeInfos.map(
@@ -384,7 +384,8 @@ tr.exportTo('tr.ui.tracks', function() {
       var bounds = track.getBoundingClientRect();
       var size = bounds.left + bounds.top + bounds.bottom + bounds.right;
       if (size === 0)
-        return this.calculateTrackY_(track.parentNode, canvasBounds);
+        return this.calculateTrackY_(
+            Polymer.dom(track).parentNode, canvasBounds);
 
       return bounds.top - canvasBounds.top + (bounds.height / 2);
     },