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

tracing/tracing/ui/tracks/thread_track.html

Index: tracing/tracing/ui/tracks/thread_track.html
diff --git a/tracing/tracing/ui/tracks/thread_track.html b/tracing/tracing/ui/tracks/thread_track.html
index aca956546b350fbc2bd5b3ed314017a66f450e04..b5c172c3b99815bf4397d40b95822fd1d62bac8f 100644
--- a/tracing/tracing/ui/tracks/thread_track.html
+++ b/tracing/tracing/ui/tracks/thread_track.html
@@ -78,7 +78,7 @@ tr.exportTo('tr.ui.tracks', function() {
         timeSlicesTrack.height = tr.ui.b.THIN_SLICE_HEIGHT + 'px';
         timeSlicesTrack.slices = this.thread_.timeSlices;
         if (timeSlicesTrack.hasVisibleContent)
-          this.appendChild(timeSlicesTrack);
+          Polymer.dom(this).appendChild(timeSlicesTrack);
       }
 
       if (this.thread_.sliceGroup.length) {
@@ -87,7 +87,7 @@ tr.exportTo('tr.ui.tracks', function() {
         track.tooltip = this.thread_.userFriendlyDetails;
         track.group = this.thread_.sliceGroup;
         if (track.hasVisibleContent)
-          this.appendChild(track);
+          Polymer.dom(this).appendChild(track);
       }
     },
 
@@ -99,7 +99,7 @@ tr.exportTo('tr.ui.tracks', function() {
         asyncTrack.group = subGroup;
         asyncTrack.heading = title;
         if (asyncTrack.hasVisibleContent)
-          this.appendChild(asyncTrack);
+          Polymer.dom(this).appendChild(asyncTrack);
       }, this);
     },
 
@@ -132,7 +132,7 @@ tr.exportTo('tr.ui.tracks', function() {
           }
           return selection;
         };
-        this.appendChild(samplesTrack);
+        Polymer.dom(this).appendChild(samplesTrack);
       }, this);
     },