GSB uses delta_hints to calculate scrolling chain.

cc/input/input_handler.h

Index: cc/input/input_handler.h
diff --git a/cc/input/input_handler.h b/cc/input/input_handler.h
index 6ffdcce57374f0effc35fac58535839c62b981a2..a32623876970dcf61096382f4dcc5d950d350091 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -131,8 +131,7 @@ class CC_EXPORT InputHandler {
 
   // Returns SCROLL_ON_IMPL_THREAD if a layer is actively being scrolled or
   // a subsequent call to ScrollAnimated can begin on the impl thread.
-  virtual ScrollStatus ScrollAnimatedBegin(
-      const gfx::Point& viewport_point) = 0;
+  virtual ScrollStatus ScrollAnimatedBegin(ScrollState* scroll_state) = 0;
 
   // Returns SCROLL_ON_IMPL_THREAD if an animation is initiated on the impl
   // thread. delayed_by is the delay that is taken into account when determining