Use Polymer.dom with many dom manipulations.

tracing/tracing/ui/base/drag_handle_test.html

Index: tracing/tracing/ui/base/drag_handle_test.html
diff --git a/tracing/tracing/ui/base/drag_handle_test.html b/tracing/tracing/ui/base/drag_handle_test.html
index e0c53b1cb114ddca8259a502317d1e8154ab3fb9..2ccd71b995d4e5d1b2e8cbd59aeb0517a9785b54 100644
--- a/tracing/tracing/ui/base/drag_handle_test.html
+++ b/tracing/tracing/ui/base/drag_handle_test.html
@@ -87,7 +87,7 @@ tr.b.unittest.testSuite(function() {
       dragHandle.forceMutationObserverFlush_();
       assert.equal(el.getLowerElHeight(), 110);
     } finally {
-      document.head.removeChild(styleEl);
+      Polymer.dom(document.head).removeChild(styleEl);
     }
   });
 });