Unify the calculation of main thread offset of sticky element

third_party/WebKit/public/platform/WebLayer.h

 /*
  * Copyright (C) 2011 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:
  *
  * 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
@@ skipping 184 matching lines @@
   // to adjust layer position during threaded scrolling.
   virtual void SetPositionConstraint(const WebLayerPositionConstraint&) = 0;
   virtual WebLayerPositionConstraint PositionConstraint() const = 0;
 
   // Sets the sticky position constraint. This will be used to adjust sticky
   // position objects during threaded scrolling.
   virtual void SetStickyPositionConstraint(
       const WebLayerStickyPositionConstraint&) = 0;
   virtual WebLayerStickyPositionConstraint StickyPositionConstraint() const = 0;
 
+  // Sets the relative position of the sticky box and its original position
+  // before scroll. This will be used to calculate the actual sticky position
+  // offset from cc side.
+  virtual void SetOffsetForStickyPosition(const WebSize&) = 0;
+  virtual WebSize OffsetForStickyPosition() const = 0;
+
   // The scroll client is notified when the scroll position of the WebLayer
   // changes. Only a single scroll client can be set for a WebLayer at a time.
   // The WebLayer does not take ownership of the scroll client, and it is the
   // responsibility of the client to reset the layer's scroll client before
   // deleting the scroll client.
   virtual void SetScrollClient(WebLayerScrollClient*) = 0;
 
   // Sets the cc-side layer client.
   virtual void SetLayerClient(cc::LayerClient*) = 0;
 
   // Gets the underlying cc layer.
   virtual const cc::Layer* CcLayer() const = 0;
   virtual cc::Layer* CcLayer() = 0;
 
   virtual void SetElementId(const cc::ElementId&) = 0;
   virtual cc::ElementId GetElementId() const = 0;
 
   virtual void SetCompositorMutableProperties(uint32_t) = 0;
   virtual uint32_t CompositorMutableProperties() const = 0;
 
   virtual void SetHasWillChangeTransformHint(bool) = 0;
 
   // Called on the scroll layer to trigger showing the overlay scrollbars.
   virtual void ShowScrollbars() = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebLayer_h