Unify the calculation of main thread offset of sticky element

third_party/WebKit/public/platform/WebLayer.h

Index: third_party/WebKit/public/platform/WebLayer.h
diff --git a/third_party/WebKit/public/platform/WebLayer.h b/third_party/WebKit/public/platform/WebLayer.h
index dc6efa8392b12f1f48e546b9196107ae7ff2c404..4aea0977fffebb3b3cdef505678427c6ff0c069e 100644
--- a/third_party/WebKit/public/platform/WebLayer.h
+++ b/third_party/WebKit/public/platform/WebLayer.h
@@ -202,6 +202,11 @@ class WebLayer {
       const WebLayerStickyPositionConstraint&) = 0;
   virtual WebLayerStickyPositionConstraint StickyPositionConstraint() const = 0;
 
+  // Sets the main thread offset applied to the sticky element. This will be
+  // used to calculate the actual sticky position offset from cc side.
+  virtual void SetStickyMainThreadOffset(const WebSize&) = 0;
+  virtual WebSize StickyMainThreadOffset() 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