DevTools: simplify & fix property overload logic

Source/devtools/front_end/sdk/CSSStyleModel.js

 /*
  * Copyright (C) 2010 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 727 matching lines @@
                 generatedProperties.push(shorthandProperty);
                 propertiesSet.add(shorthand);
             }
         }
         this._allProperties = this._allProperties.concat(generatedProperties);
     },
 
     /**
      * @return {!Array.<!WebInspector.CSSProperty>}
      */
-    leadingProperties: function()
+    _computeLeadingProperties: function()
     {
         /**
          * @param {!WebInspector.CSSProperty} property
          * @return {boolean}
          */
         function propertyHasRange(property)
         {
             return !!property.range;
         }
 
@@ skipping 11 matching lines @@
                 }
             }
             if (!belongToAnyShorthand)
                 leadingProperties.push(property);
         }
 
         return leadingProperties;
     },
 
     /**
+     * @return {!Array.<!WebInspector.CSSProperty>}
+     */
+    leadingProperties: function()
+    {
+        if (!this._leadingProperties)
+            this._leadingProperties = this._computeLeadingProperties();
+        return this._leadingProperties;
+    },
+
+    /**
      * @return {!WebInspector.Target}
      */
     target: function()
     {
         return this._cssModel.target();
     },
 
     /**
      * @return {!WebInspector.CSSStyleModel}
      */
@@ skipping 1204 matching lines @@
  * @constructor
  * @param {?WebInspector.CSSStyleDeclaration} inlineStyle
  * @param {?WebInspector.CSSStyleDeclaration} attributesStyle
  */
 WebInspector.CSSStyleModel.InlineStyleResult = function(inlineStyle, attributesStyle)
 {
     this.inlineStyle = inlineStyle;
     this.attributesStyle = attributesStyle;
 }