[polymer] Switches .appendChild() to Polymer.dom()...appendChild()

tracing/tracing/ui/base/info_bar.html

Index: tracing/tracing/ui/base/info_bar.html
diff --git a/tracing/tracing/ui/base/info_bar.html b/tracing/tracing/ui/base/info_bar.html
index e239936caef72d0fc6ced1d628f25fa15293013a..49a00f09cbcb21ff42c63dcb984c9c4a69dee9a7 100644
--- a/tracing/tracing/ui/base/info_bar.html
+++ b/tracing/tracing/ui/base/info_bar.html
@@ -77,7 +77,7 @@ Polymer({
     var button = document.createElement('button');
     button.textContent = text;
     button.addEventListener('click', clickCallback);
-    this.buttonsEl_.appendChild(button);
+    Polymer.dom(this.buttonsEl_).appendChild(button);
     return button;
   }
 });