DevTools: use target-based model accessors only.

Source/devtools/front_end/sdk/ContentProviders.js

 /*
  * Copyright (C) 2011 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 209 matching lines @@
     {
         return this._contentType;
     },
 
     /**
      * @override
      * @param {function(?string)} callback
      */
     requestContent: function(callback)
     {
-        this._target.networkAgent().loadResourceForFrontend(WebInspector.resourceTreeModel.mainFrame.id, this._sourceURL, undefined, contentLoaded.bind(this));
+        this._target.networkAgent().loadResourceForFrontend(this._target.resourceTreeModel.mainFrame.id, this._sourceURL, undefined, contentLoaded.bind(this));
 
         /**
          * @param {?Protocol.Error} error
          * @param {number} statusCode
          * @param {!NetworkAgent.Headers} headers
          * @param {string} content
          * @this {WebInspector.CompilerSourceMappingContentProvider}
          */
         function contentLoaded(error, statusCode, headers, content)
         {
@@ skipping 25 matching lines @@
         {
             if (typeof content !== "string") {
                 callback([]);
                 return;
             }
 
             callback(WebInspector.ContentProvider.performSearchInContent(content, query, caseSensitive, isRegex));
         }
     }
 }