Mark FrameHost::deviceScaleFactor as deprecated.

third_party/WebKit/Source/core/frame/FrameHost.h

 /*
  * 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 72 matching lines @@
 
     UseCounter& useCounter();
     const UseCounter& useCounter() const;
 
     Deprecation& deprecation();
     const Deprecation& deprecation() const;
 
     // Corresponds to pixel density of the device where this Page is
     // being displayed. In multi-monitor setups this can vary between pages.
     // This value does not account for Page zoom, use LocalFrame::devicePixelRatio instead.
-    float deviceScaleFactor() const;
+    // This is to be deprecated. Use this with caution.
+    // 1) If you need to scale the content per device scale factor, this is still valid.
+    //    In use-zoom-for-dsf mode, this is always 1, and will be remove when transition is complete.
+    // 2) If you want to compute the device related measure (such as device pixel height, or the scale factor for drag image),
+    //    use ChromeClient::screenInfo() instead.
+    float deviceScaleFactorDeprecated() const;
 
     RootScroller* rootScroller();
     const RootScroller* rootScroller() const;
 
     TopControls& topControls();
     const TopControls& topControls() const;
 
     OverscrollController& overscrollController();
     const OverscrollController& overscrollController() const;
 
@@ skipping 38 matching lines @@
     const Member<EventHandlerRegistry> m_eventHandlerRegistry;
     const Member<ConsoleMessageStorage> m_consoleMessageStorage;
 
     AtomicString m_overrideEncoding;
     int m_subframeCount;
 };
 
 } // namespace blink
 
 #endif // FrameHost_h