DevTools: [JSDoc] Fix invalid @param and @return annotations

Source/devtools/front_end/ScreencastView.js

 /*
  * Copyright (C) 2013 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 496 matching lines @@
      */
     _convertIntoScreenSpace: function(event)
     {
         var position = this._zoomIntoScreenSpace(event);
         position.y = Math.round(position.y - this._screenOffsetTop);
         return position;
     },
 
     /**
      * @param {!Event} event
-     * @return number
+     * @return {number}
      */
     _modifiersForEvent: function(event)
     {
         var modifiers = 0;
         if (event.altKey)
             modifiers = 1;
         if (event.ctrlKey)
             modifiers += 2;
         if (event.metaKey)
             modifiers += 4;
@@ skipping 486 matching lines @@
           return;
         this._maxDisplayedProgress = progress;
         this._displayProgress(progress);
     },
 
     _displayProgress: function(progress)
     {
         this._element.style.width = (100 * progress) + "%";
     }
 };