Use Polymer.dom with many dom manipulations.

tracing/tracing/ui/base/chart_base_2d.html

Index: tracing/tracing/ui/base/chart_base_2d.html
diff --git a/tracing/tracing/ui/base/chart_base_2d.html b/tracing/tracing/ui/base/chart_base_2d.html
index 5e32e3b95d516626f049096402066625d52e7041..a68efda1ce0f5427279185929e0e21bf79947a89 100644
--- a/tracing/tracing/ui/base/chart_base_2d.html
+++ b/tracing/tracing/ui/base/chart_base_2d.html
@@ -32,7 +32,7 @@ tr.exportTo('tr.ui.b', function() {
 
     decorate: function() {
       ChartBase.prototype.decorate.call(this);
-      this.classList.add('chart-base-2d');
+      Polymer.dom(this).classList.add('chart-base-2d');
       this.xScale_ = d3.scale.linear();
       this.yScale_ = d3.scale.linear();
       this.isYLogScale_ = false;
@@ -352,7 +352,7 @@ tr.exportTo('tr.ui.b', function() {
       mouseEvent.stopPropagation();
       var dataEvent = new tr.b.Event('item-mousedown');
       dataEvent.button = mouseEvent.button;
-      this.classList.add('updating-brushing-state');
+      Polymer.dom(this).classList.add('updating-brushing-state');
       this.prepareDataEvent_(mouseEvent, dataEvent);
       this.dispatchEvent(dataEvent);
     },
@@ -375,7 +375,7 @@ tr.exportTo('tr.ui.b', function() {
       dataEvent.button = button;
       this.prepareDataEvent_(mouseEvent, dataEvent);
       this.dispatchEvent(dataEvent);
-      this.classList.remove('updating-brushing-state');
+      Polymer.dom(this).classList.remove('updating-brushing-state');
     }
   };