[polymer] Replaces this.appendChild with Polymer.dom(this).appendChild

tracing/tracing/ui/tracks/cpu_track.html

Index: tracing/tracing/ui/tracks/cpu_track.html
diff --git a/tracing/tracing/ui/tracks/cpu_track.html b/tracing/tracing/ui/tracks/cpu_track.html
index 84b7afe6582a62e9a54f597c95928f180e14aad8..0bb4f1fdf442f0a3f87941cebd3ba41b4ddaeae6 100644
--- a/tracing/tracing/ui/tracks/cpu_track.html
+++ b/tracing/tracing/ui/tracks/cpu_track.html
@@ -81,7 +81,7 @@ tr.exportTo('tr.ui.tracks', function() {
         var track = new tr.ui.tracks.SliceTrack(this.viewport);
         track.slices = slices;
         track.heading = this.cpu_.userFriendlyName + ':';
-        this.appendChild(track);
+        Polymer.dom(this).appendChild(track);
       }
 
       if (this.detailedMode_) {
@@ -93,7 +93,7 @@ tr.exportTo('tr.ui.tracks', function() {
           track.heading = this.cpu_.userFriendlyName + ' ' +
               counter.name + ':';
           track.counter = counter;
-          this.appendChild(track);
+          Polymer.dom(this).appendChild(track);
         }
       }
     },
@@ -127,7 +127,7 @@ tr.exportTo('tr.ui.tracks', function() {
           }
           return selection;
         };
-        this.appendChild(samplesTrack);
+        Polymer.dom(this).appendChild(samplesTrack);
       }, this);
     }
   };