Use Polymer.dom with many dom manipulations.

tracing/tracing/base/unittest/suite_loader.html

Index: tracing/tracing/base/unittest/suite_loader.html
diff --git a/tracing/tracing/base/unittest/suite_loader.html b/tracing/tracing/base/unittest/suite_loader.html
index e72bcd9c1c85af6a20cf112f50260cf0d4f8f9ad..655bb4003c4d1c0d3917897199600a7655b19363 100644
--- a/tracing/tracing/base/unittest/suite_loader.html
+++ b/tracing/tracing/base/unittest/suite_loader.html
@@ -22,8 +22,8 @@ tr.exportTo('tr.b.unittest', function() {
       return new Promise(function(resolve, reject) {
         var importEl = document.createElement('link');
         importEl.moduleName = moduleName;
-        importEl.setAttribute('rel', 'import');
-        importEl.setAttribute('href', testRelpath);
+        Polymer.dom(importEl).setAttribute('rel', 'import');
+        Polymer.dom(importEl).setAttribute('href', testRelpath);
 
         importEl.addEventListener('load', function() {
           resolve({testRelpath: testRelpath,