Use Polymer.dom with many dom manipulations.

tracing/tracing/ui/side_panel/side_panel_container.html

Index: tracing/tracing/ui/side_panel/side_panel_container.html
diff --git a/tracing/tracing/ui/side_panel/side_panel_container.html b/tracing/tracing/ui/side_panel/side_panel_container.html
index af82c2cd0b78256f7d94327259ddcc2ba90f3ca4..743c95338ad7a478b7196fe48410a6d88fdbad85 100644
--- a/tracing/tracing/ui/side_panel/side_panel_container.html
+++ b/tracing/tracing/ui/side_panel/side_panel_container.html
@@ -149,20 +149,20 @@ Polymer({
       throw new Error('Cannot activate panel: does not support this model');
 
     if (this.activePanelType) {
-      this.getLabelElementForPanelType_(
-          this.activePanelType).removeAttribute('selected');
+      Polymer.dom(this.getLabelElementForPanelType_(
+          this.activePanelType)).removeAttribute('selected');
     }
     this.activePanelContainer_.textContent = '';
 
     if (panelType === undefined) {
-      this.removeAttribute('expanded');
+      Polymer.dom(this).removeAttribute('expanded');
       this.activePanelType_ = undefined;
       return;
     }
 
-    this.getLabelElementForPanelType_(panelType).
+    Polymer.dom(this.getLabelElementForPanelType_(panelType)).
         setAttribute('selected', true);
-    this.setAttribute('expanded', true);
+    Polymer.dom(this).setAttribute('expanded', true);
 
     Polymer.dom(this.activePanelContainer_).appendChild(panel);
     panel.rangeOfInterest = this.rangeOfInterest_;
@@ -205,7 +205,7 @@ Polymer({
       var supported = panel.supportsModel(this.model);
       if (this.model && supported.supported) {
         supportedPanelTypes.push(panelType);
-        labelEl.setAttribute('enabled', true);
+        Polymer.dom(labelEl).setAttribute('enabled', true);
         labelEl.addEventListener('click', function() {
           this.activePanelType =
               this.activePanelType === panelType ? undefined : panelType;
@@ -222,10 +222,10 @@ Polymer({
     if (previouslyActivePanelType &&
         supportedPanelTypes.indexOf(previouslyActivePanelType) != -1) {
       this.activePanelType = previouslyActivePanelType;
-      this.setAttribute('expanded', true);
+      Polymer.dom(this).setAttribute('expanded', true);
     } else {
       this.activePanelContainer_.textContent = '';
-      this.removeAttribute('expanded');
+      Polymer.dom(this).removeAttribute('expanded');
     }
   },