Add dedicated windowToViewport method

third_party/WebKit/Source/platform/HostWindow.h

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
     HostWindow() { }
     virtual ~HostWindow() { }
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
     // Requests the host invalidate the contents.
     virtual void invalidateRect(const IntRect& updateRect) = 0;
 
     // Converts the rect from the viewport coordinates to screen coordinates.
     virtual IntRect viewportToScreen(const IntRect&) const = 0;
 
-    // Converts the length from the screen coordinates to the viewport coordinates.
-    virtual float screenToViewport(float length) const = 0;
+    // Converts the rect from the window coordinates to the viewport coordinates.
+    virtual FloatRect windowToViewport(const FloatRect&) const = 0;
 
     virtual void scheduleAnimation(Widget*) = 0;
 };
 
 } // namespace blink
 
 #endif // HostWindow_h