Generalize browser controls adjustment for arbitrary scrollers.

third_party/WebKit/Source/core/frame/VisualViewport.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 128 matching lines @@
   IntPoint clampDocumentOffsetAtScale(const IntPoint& offset, float scale);
 
   // FIXME: This is kind of a hack. Ideally, we would just resize the
   // viewports to account for browser controls. However, FrameView includes much
   // more than just scrolling so we can't simply resize it without incurring
   // all sorts of side-effects. Until we can seperate out the scrollability
   // aspect from FrameView, we use this method to let VisualViewport make the
   // necessary adjustments so that we don't incorrectly clamp scroll offsets
   // coming from the compositor. crbug.com/422328
   void setBrowserControlsAdjustment(float);
+  float browserControlsAdjustment() const;
 
   // Adjust the viewport's offset so that it remains bounded by the outer
   // viepwort.
   void clampToBoundaries();
 
   FloatRect viewportToRootFrame(const FloatRect&) const;
   IntRect viewportToRootFrame(const IntRect&) const;
   FloatRect rootFrameToViewport(const FloatRect&) const;
   IntRect rootFrameToViewport(const IntRect&) const;
 
@@ skipping 108 matching lines @@
   float m_scale;
   IntSize m_size;
   float m_browserControlsAdjustment;
   float m_maxPageScale;
   bool m_trackPinchZoomStatsForPage;
 };
 
 }  // namespace blink
 
 #endif  // VisualViewport_h