Introduce painted-device-scale-factor and use it when --enable-use-zoom-for-dsf is specified.

third_party/WebKit/public/web/WebView.h

 /*
  * Copyright (C) 2009, 2010, 2011, 2012 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 275 matching lines @@
 
     // Sets the display mode of the web app.
     virtual void setDisplayMode(WebDisplayMode) = 0;
 
     // The ratio of the current device's screen DPI to the target device's screen DPI.
     virtual float deviceScaleFactor() const = 0;
 
     // Sets the ratio as computed by computePageScaleConstraints.
     virtual void setDeviceScaleFactor(float) = 0;
 
+    // Enables the mode to use zoom to implement device scale factor.
+    virtual void enableUseZoomForDeviceScaleFactor() = 0;
+
     // Set and reset the device color profile.
     virtual void setDeviceColorProfile(const WebVector<char>&) = 0;
     virtual void resetDeviceColorProfile() = 0;
 
     // Auto-Resize -----------------------------------------------------------
 
     // In auto-resize mode, the view is automatically adjusted to fit the html
     // content within the given bounds.
     virtual void enableAutoResizeMode(
         const WebSize& minSize,
@@ skipping 174 matching lines @@
     // context's ability to deal with that failure gracefully can be tested.
     virtual void forceNextDrawingBufferCreationToFail() = 0;
 
 protected:
     ~WebView() {}
 };
 
 } // namespace blink
 
 #endif