Refactor compositor event handling path to be callback-based

ui/events/blink/input_handler_proxy_client.h

Index: ui/events/blink/input_handler_proxy_client.h
diff --git a/ui/events/blink/input_handler_proxy_client.h b/ui/events/blink/input_handler_proxy_client.h
index efc24ed6d17d4a83b8879422c96db83481f7d89a..ba9fd8246bc297712bc4240f4b8fbf3a9989b765 100644
--- a/ui/events/blink/input_handler_proxy_client.h
+++ b/ui/events/blink/input_handler_proxy_client.h
@@ -32,11 +32,11 @@ class InputHandlerProxyClient {
       const blink::WebFloatPoint& velocity,
       const blink::WebSize& cumulative_scroll) = 0;
 
-  virtual void DidOverscroll(
-      const gfx::Vector2dF& accumulated_overscroll,
-      const gfx::Vector2dF& latest_overscroll_delta,
-      const gfx::Vector2dF& current_fling_velocity,
-      const gfx::PointF& causal_event_viewport_point) = 0;
+  virtual void DidOverscroll(const gfx::Vector2dF& accumulated_overscroll,
+                             const gfx::Vector2dF& latest_overscroll_delta,
+                             const gfx::Vector2dF& current_fling_velocity,
+                             const gfx::PointF& causal_event_viewport_point,
+                             bool bundle_ack_with_triggering_event) = 0;
 
   virtual void DidStartFlinging() = 0;