Refactor compositor event handling path to be callback-based

content/renderer/input/input_handler_manager.h

Index: content/renderer/input/input_handler_manager.h
diff --git a/content/renderer/input/input_handler_manager.h b/content/renderer/input/input_handler_manager.h
index f9313666d731f6fbba8af2a00e3cb0cc942bef94..b76420f285fbc75ddbe4deee24aa1fe4c908b0f0 100644
--- a/content/renderer/input/input_handler_manager.h
+++ b/content/renderer/input/input_handler_manager.h
@@ -11,6 +11,7 @@
 #include "content/common/content_export.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "content/renderer/render_view_impl.h"
+#include "ui/events/blink/input_handler_proxy.h"
 
 namespace base {
 class SingleThreadTaskRunner;
@@ -79,11 +80,16 @@ class CONTENT_EXPORT InputHandlerManager {
   // Callback only from the compositor's thread.
   void RemoveInputHandler(int routing_id);
 
+  using InputEventAckStateCallback =
+      base::Callback<void(InputEventAckState,
+                          ui::ScopedWebInputEvent,
+                          const ui::LatencyInfo&,
+                          std::unique_ptr<ui::DidOverscrollParams>)>;
   // Called from the compositor's thread.
-  virtual InputEventAckState HandleInputEvent(
-      int routing_id,
-      const blink::WebInputEvent* input_event,
-      ui::LatencyInfo* latency_info);
+  virtual void HandleInputEvent(int routing_id,
+                                ui::ScopedWebInputEvent input_event,
+                                const ui::LatencyInfo& latency_info,
+                                const InputEventAckStateCallback& callback);
 
   // Called from the compositor's thread.
   void DidOverscroll(int routing_id, const ui::DidOverscrollParams& params);

[chongz, 2016/08/30 17:58:03]

I cannot fully merge |DidOverscroll| and |DidHandleInputEvent| into a single
callback as other overscroll sources require the client interface.

A compromise solution is to rename |DidHandleInputEvent| =>
|DidHandleInputEventAndOverscroll|, such that:
  1. All InputEvent triggered overscroll will go into
|DidHandleInputEventAndOverscroll|
  2. Other sources of overscroll with go into |DidOverscroll|

Please see CL description for more detailed event path.

@@ -120,6 +126,14 @@ class CONTENT_EXPORT InputHandlerManager {
       const blink::WebGestureEvent& gesture_event,
       const cc::InputHandlerScrollResult& scroll_result);
 
+  using EventDisposition = ui::InputHandlerProxy::EventDisposition;
+  void DidHandleInputEventAndOverscroll(
+      const InputEventAckStateCallback& callback,
+      EventDisposition event_disposition,
+      ui::ScopedWebInputEvent input_event,
+      const ui::LatencyInfo& latency_info,
+      std::unique_ptr<ui::DidOverscrollParams> overscroll_params);
+
   typedef base::ScopedPtrHashMap<int,  // routing_id
                                  std::unique_ptr<InputHandlerWrapper>>
       InputHandlerMap;