Don't use getPropertyCSSValue in treeoutline.js

Source/devtools/front_end/ui/treeoutline.js

 /*
  * Copyright (C) 2007 Apple 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 1001 matching lines @@
 
     return this.parent;
 }
 
 /**
  * @return {boolean}
  */
 TreeElement.prototype.isEventWithinDisclosureTriangle = function(event)
 {
     // FIXME: We should not use getComputedStyle(). For that we need to get rid of using ::before for disclosure triangle. (http://webk.it/74446)
-    var paddingLeftValue = window.getComputedStyle(this._listItemNode).getPropertyCSSValue("padding-left");
-    var computedLeftPadding = paddingLeftValue ? paddingLeftValue.getFloatValue(CSSPrimitiveValue.CSS_PX) : 0;
+    var paddingLeftValue = window.getComputedStyle(this._listItemNode).paddingLeft;
+    console.assert(paddingLeftValue.endsWith("px"));
+    var computedLeftPadding = parseFloat(paddingLeftValue, 10);
     var left = this._listItemNode.totalOffsetLeft() + computedLeftPadding;
     return event.pageX >= left && event.pageX <= left + this.arrowToggleWidth && this.hasChildren;
 }