[DevTools] Explicitly enable/disable Page.viewportChanged protocol event.

Source/devtools/front_end/sdk/ResourceTreeModel.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 454 matching lines @@
      * @param {boolean=} ignoreCache
      * @param {string=} scriptToEvaluateOnLoad
      * @param {string=} scriptPreprocessor
      */
     reloadPage: function(ignoreCache, scriptToEvaluateOnLoad, scriptPreprocessor)
     {
         this.dispatchEventToListeners(WebInspector.ResourceTreeModel.EventTypes.WillReloadPage);
         this._agent.reload(ignoreCache, scriptToEvaluateOnLoad, scriptPreprocessor);
     },
 
+    /**
+     * @param {boolean} enabled
+     */
+    setViewportChangedEventEnabled: function(enabled)
+    {
+        this._agent.setViewportChangedEventEnabled(enabled);
+    },
+
     __proto__: WebInspector.TargetAwareObject.prototype
 }
 
 /**
  * @constructor
  * @param {!WebInspector.ResourceTreeModel} model
  * @param {?WebInspector.ResourceTreeFrame} parentFrame
  * @param {!PageAgent.FrameId} frameId
  * @param {!PageAgent.Frame=} payload
  */
@@ skipping 335 matching lines @@
     viewportChanged: function(viewport)
     {
         this._resourceTreeModel.dispatchEventToListeners(WebInspector.ResourceTreeModel.EventTypes.ViewportChanged, viewport);
     }
 }
 
 /**
  * @type {!WebInspector.ResourceTreeModel}
  */
 WebInspector.resourceTreeModel;