Revert of [DevTools] Remove edited scripts from debugger agent, move knowledge to frontend.

Source/devtools/front_end/workspace/UISourceCode.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 444 matching lines @@
      * @return {string}
      */
     workingCopy: function()
     {
         if (this._workingCopyGetter) {
             this._workingCopy = this._workingCopyGetter();
             delete this._workingCopyGetter;
         }
         if (this.isDirty())
             return this._workingCopy;
-        return this._content || "";
+        return this._content;
     },
 
     resetWorkingCopy: function()
     {
         this._innerResetWorkingCopy();
         this.dispatchEventToListeners(WebInspector.UISourceCode.Events.WorkingCopyChanged);
     },
 
     _innerResetWorkingCopy: function()
     {
@@ skipping 243 matching lines @@
      * @param {string} query
      * @param {boolean} caseSensitive
      * @param {boolean} isRegex
      * @param {function(!Array.<!WebInspector.ContentProvider.SearchMatch>)} callback
      */
     searchInContent: function(query, caseSensitive, isRegex, callback)
     {
         callback([]);
     }
 }