Use Polymer.dom with many dom manipulations.

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

Index: tracing/tracing/ui/extras/chrome/cc/picture_ops_chart_view.html
diff --git a/tracing/tracing/ui/extras/chrome/cc/picture_ops_chart_view.html b/tracing/tracing/ui/extras/chrome/cc/picture_ops_chart_view.html
index dfb554bdf1b12e051d0169bd93ad2e44ee4cfae0..fe71fc87735b86979e404ab158c15a2f1e0e4850 100644
--- a/tracing/tracing/ui/extras/chrome/cc/picture_ops_chart_view.html
+++ b/tracing/tracing/ui/extras/chrome/cc/picture_ops_chart_view.html
@@ -69,7 +69,8 @@ tr.exportTo('tr.ui.e.chrome.cc', function() {
           this, 'usePercentileScale',
           'PictureOpsChartView.usePercentileScale', false,
           'Limit to 95%-ile');
-      this.usePercentileScaleCheckbox_.classList.add('use-percentile-scale');
+      Polymer.dom(this.usePercentileScaleCheckbox_).classList.add(
+          'use-percentile-scale');
       Polymer.dom(this).appendChild(this.usePercentileScaleCheckbox_);
     },