Turn on harmony arrays and regexp.

sky/examples/fps-counter.sky

 <!--
 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="/sky/framework/sky-element/sky-element.sky" as="SkyElement" />
 
 <sky-element name="fps-counter" attributes="showHistory:boolean">
 <template>
   <template if="{{ showHistory }}">
     <template repeat="{{ history }}">
       <div>{{ }} ms</div>
     </template>
     <div>max = {{ max }} ms</div>
   </template>
   <div>fps = {{ framerate }} Hz</div>
 </template>
 <script>
 var kMaxDeltaLength = 10;
 
 module.exports = class extends SkyElement {
   created() {
     this.framerate = "...";
     this.max = 0;
     this.lastTimeStamp = 0;
     this.rafId = 0;
     this.currentDeltaIndex = 0;
     this.deltas = new Array(kMaxDeltaLength);
-    for (var i = 0; i < kMaxDeltaLength; ++i)
-      this.deltas[i] = 0;
+    this.deltas.fill(0);
     this.history = new Array(kMaxDeltaLength);
-    for (var i = 0; i < kMaxDeltaLength; ++i)
-      this.history[i] = 0;
+    this.history.fill(0);
   }
   attached() {
     this.scheduleTick();
   }
   detached() {
     cancelAnimationFrame(this.rafId);
     this.rafId = 0;
   }
   scheduleTick() {
     this.rafId = requestAnimationFrame(this.tick.bind(this));  
@@ skipping 11 matching lines @@
       this.history[i] = value.toFixed(2);
     }
     var sum = this.deltas.reduce(function(a, b) { return a + b }, 0);
     var avg = sum / kMaxDeltaLength;
     this.framerate = (1000 / avg).toFixed(2);
     this.max = Math.max(delta, this.max).toFixed(2);
   }
 }.register();
 </script>
 </sky-element>