[Devtools] Lazily build reverse mappings

third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.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 194 matching lines @@
             this.dispatchEventToListeners(WebInspector.CSSModel.Events.SourceMapAttached, header);
         }
     },
 
     /**
      * @param {!WebInspector.SourceMap} sourceMap
      * @return {?Runtime.Extension}
      */
     _factoryForSourceMap: function(sourceMap)
     {
-        var sourceExtensions = new Set(sourceMap.sourceURLs().map(url => WebInspector.ParsedURL.extractExtension(url)));
+        var sourceExtensions = new Set();
+        for (var url of sourceMap.sourceURLs())
+            sourceExtensions.add(WebInspector.ParsedURL.extractExtension(url));
         for (var runtimeExtension of self.runtime.extensions(WebInspector.SourceMapFactory)) {
             var supportedExtensions = new Set(runtimeExtension.descriptor()["extensions"]);
             if (supportedExtensions.containsAll(sourceExtensions))
                 return runtimeExtension;
         }
         return null;
     },
 
     /**
      * @param {!WebInspector.CSSStyleSheetHeader} header
@@ skipping 1003 matching lines @@
 /**
  * @constructor
  * @param {?WebInspector.CSSStyleDeclaration} inlineStyle
  * @param {?WebInspector.CSSStyleDeclaration} attributesStyle
  */
 WebInspector.CSSModel.InlineStyleResult = function(inlineStyle, attributesStyle)
 {
     this.inlineStyle = inlineStyle;
     this.attributesStyle = attributesStyle;
 }