Use Polymer.dom with many dom manipulations.

tracing/tracing/ui/base/tab_view.html

Index: tracing/tracing/ui/base/tab_view.html
diff --git a/tracing/tracing/ui/base/tab_view.html b/tracing/tracing/ui/base/tab_view.html
index 48667a7075fe3f9ff3d2605f0932a1a7d032b6bc..8412d282c34c11ccf147a4b7330760e2c362d0a7 100644
--- a/tracing/tracing/ui/base/tab_view.html
+++ b/tracing/tracing/ui/base/tab_view.html
@@ -196,17 +196,17 @@ window.TracingAnalysisTabView = Polymer({
   },
 
   get tabsHidden() {
-    var ts = this.shadowRoot.querySelector('tab-strip');
+    var ts = Polymer.dom(this.root).querySelector('tab-strip');
     return ts.hasAttribute('tabs-hidden');
   },
 
   set tabsHidden(tabsHidden) {
     tabsHidden = !!tabsHidden;
-    var ts = this.shadowRoot.querySelector('tab-strip');
+    var ts = Polymer.dom(this.root).querySelector('tab-strip');
     if (tabsHidden)
-      ts.setAttribute('tabs-hidden', true);
+      Polymer.dom(ts).setAttribute('tabs-hidden', true);
     else
-      ts.removeAttribute('tabs-hidden');
+      Polymer.dom(ts).removeAttribute('tabs-hidden');
   },
 
   get tabs() {
@@ -239,7 +239,7 @@ window.TracingAnalysisTabView = Polymer({
       // selected tab, mark the child as the selected tab, otherwise keep
       // the previous selection.
       if (this.selectedTab_)
-        child.removeAttribute('selected');
+        Polymer.dom(child).removeAttribute('selected');
       else
         this.setSelectedTabById_(tabObject.id);
     }
@@ -295,7 +295,7 @@ window.TracingAnalysisTabView = Polymer({
           this.clearSelectedTab_();
           this.fire('selected-tab-change');
         }
-        child.removeAttribute('selected');
+        Polymer.dom(child).removeAttribute('selected');
         delete child.selected;
         // Remove the observer since we no longer care about this child.
         this.splice('tabs_', i, 1);
@@ -389,7 +389,7 @@ window.TracingAnalysisTabView = Polymer({
     this.selectedTab_ = this.tabs_[id];
     // Disconnect observer while we mutate the child.
     this.selectedTab_.observers.forAttributeSelected.disconnect();
-    this.selectedTab_.content.setAttribute('selected', 'selected');
+    Polymer.dom(this.selectedTab_.content).setAttribute('selected', 'selected');
     // Reconnect the observer to watch for changes in the future.
     this.selectedTab_.observers.forAttributeSelected.observe(
         this.selectedTab_.content, { attributeFilter: ['selected'] });
@@ -427,7 +427,7 @@ window.TracingAnalysisTabView = Polymer({
     if (this.selectedTab_) {
       // Disconnect observer while we mutate the child.
       this.selectedTab_.observers.forAttributeSelected.disconnect();
-      this.selectedTab_.content.removeAttribute('selected');
+      Polymer.dom(this.selectedTab_.content).removeAttribute('selected');
       // Reconnect the observer to watch for changes in the future.
       this.selectedTab_.observers.forAttributeSelected.observe(
           this.selectedTab_.content, { attributeFilter: ['selected'] });