Clean up perftesthelper.js style

tools/perf/page_sets/tough_animation_cases/balls_css_keyframe_animations.html

 <!--
 Copyright (c) 2012 Cameron Adams. All rights reserved.
 Copyright (c) 2012 Code Aurora Forum. All rights reserved.
 Copyright (C) 2013 Google Inc. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
 met:
     * Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
@@ skipping 37 matching lines @@
     padding: 0;
 }
 
 span {
     position: absolute;
     width: 12px;
     height: 12px;
     border-radius: 6px;
 }
 </style>
-<script src="resources/perftesthelper.js"></script>
+<script src="resources/perf_test_helper.js"></script>
 <script>
 var measurementReady = false;
 var stageWidth = 600;
 var stageHeight = 600;
 var maxParticles = 2500;
 var minVelocity = 50;
 var maxVelocity = 500;
 var particleRadius = 6;
 var colors = ["#cc0000", "#ffcc00", "#aaff00", "#0099cc", "#194c99", "#661999"];
 var animationDuration = 10;
@@ skipping 103 matching lines @@
         document.body.removeChild(domNode);
     }
 
     this.start = start;
     this.destroy = destroy;
 }
 </script>
 <style id="keyframes"></style>
 </head>
 </html>