DevTools: optimize screencast for slower devices.

third_party/WebKit/Source/devtools/front_end/screencast/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 132 matching lines @@
         this._target.pageAgent().stopScreencast();
         this._target.emulationAgent().setTouchEmulationEnabled(false);
         this._domModel.setHighlighter(null);
     },
 
     /**
      * @param {!WebInspector.Event} event
      */
     _screencastFrame: function(event)
     {
+        this._target.pageAgent().screencastFrameAck();
+
         var metadata = /** type {PageAgent.ScreencastFrameMetadata} */(event.data.metadata);
         var base64Data = /** type {string} */(event.data.data);
         this._imageElement.src = "data:image/jpg;base64," + base64Data;
         this._pageScaleFactor = metadata.pageScaleFactor;
         this._screenOffsetTop = metadata.offsetTop;
         this._scrollOffsetX = metadata.scrollOffsetX;
         this._scrollOffsetY = metadata.scrollOffsetY;
 
-        if (event.data.frameNumber)
-            this._target.pageAgent().screencastFrameAck(event.data.frameNumber);
-
         var deviceSizeRatio = metadata.deviceHeight / metadata.deviceWidth;
         var dimensionsCSS = this._viewportDimensions();
 
         this._imageZoom = Math.min(dimensionsCSS.width / this._imageElement.naturalWidth, dimensionsCSS.height / (this._imageElement.naturalWidth * deviceSizeRatio));
         this._viewportElement.classList.remove("hidden");
         var bordersSize = WebInspector.ScreencastView._bordersSize;
         if (this._imageZoom < 1.01 / window.devicePixelRatio)
             this._imageZoom = 1 / window.devicePixelRatio;
         this._screenZoom = this._imageElement.naturalWidth * this._imageZoom / metadata.deviceWidth;
         this._viewportElement.style.width = metadata.deviceWidth * this._screenZoom + bordersSize + "px";
@@ skipping 692 matching lines @@
           return;
         this._maxDisplayedProgress = progress;
         this._displayProgress(progress);
     },
 
     _displayProgress: function(progress)
     {
         this._element.style.width = (100 * progress) + "%";
     }
 };