Implement position: sticky updates on compositor

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 340b05e64dfb2a50de9049766441aebfceeadce5..095267ce51ca6253ba7e0ba75e9bbfc4ca4a7fa3 100644
--- a/third_party/WebKit/public/platform/WebLayer.h
+++ b/third_party/WebKit/public/platform/WebLayer.h
@@ -53,6 +53,7 @@ namespace blink {
 class WebLayerScrollClient;
 struct WebFloatPoint;
 struct WebLayerPositionConstraint;
+struct WebLayerStickyPositionConstraint;
 
 class WebLayer {
 public:
@@ -188,6 +189,11 @@ public:
     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;
+
     // 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