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

third_party/WebKit/Source/web/WebViewImpl.h

 /*
  * Copyright (C) 2010 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 192 matching lines @@
     WebFloatPoint visualViewportOffset() const override;
     WebFloatPoint pinchViewportOffset() const override;
     WebFloatSize visualViewportSize() const override;
     void resetScrollAndScaleState() override;
     void setIgnoreViewportTagScaleLimits(bool) override;
     WebSize contentsPreferredMinimumSize() override;
     void setDisplayMode(WebDisplayMode) override;
 
     float deviceScaleFactor() const override;
     void setDeviceScaleFactor(float) override;
+    void setZoomFactorForDeviceScaleFactor(float) override;
+
     void setDeviceColorProfile(const WebVector<char>&) override;
     void resetDeviceColorProfile() override;
 
     void enableAutoResizeMode(
         const WebSize& minSize,
         const WebSize& maxSize) override;
     void disableAutoResizeMode() override;
     void performMediaPlayerAction(
         const WebMediaPlayerAction& action,
         const WebPoint& location) override;
@@ skipping 422 matching lines @@
     WebPoint m_lastMouseDownPoint;
 
     // Keeps track of the current zoom level. 0 means no zoom, positive numbers
     // mean zoom in, negative numbers mean zoom out.
     double m_zoomLevel;
 
     double m_minimumZoomLevel;
 
     double m_maximumZoomLevel;
 
+    // Additional zoom factor used to scale the content by device scale factor.
+    double m_zoomFactorForDeviceScaleFactor;
+
     // This value, when multiplied by the font scale factor, gives the maximum
     // page scale that can result from automatic zooms.
     float m_maximumLegibleScale;
 
     // The scale moved to by the latest double tap zoom, if any.
     float m_doubleTapZoomPageScaleFactor;
     // Have we sent a double-tap zoom and not yet heard back the scale?
     bool m_doubleTapZoomPending;
 
     // Used for testing purposes.
@@ skipping 86 matching lines @@
 };
 
 DEFINE_TYPE_CASTS(WebViewImpl, WebWidget, widget, widget->isWebView(), widget.isWebView());
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 } // namespace blink
 
 #endif