Refactor compositor event handling path to be callback-based

content/renderer/input/input_handler_manager_client.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_INPUT_INPUT_HANDLER_MANAGER_CLIENT_H_
 #define CONTENT_RENDERER_INPUT_INPUT_HANDLER_MANAGER_CLIENT_H_
 
 #include "base/callback.h"
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "content/common/content_export.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/gfx/geometry/vector2d_f.h"
 
-namespace ui {
-class LatencyInfo;
-struct DidOverscrollParams;
-}
-
 namespace cc {
 class InputHandler;
 }
 
 namespace ui {
 class SynchronousInputHandlerProxy;
+struct DidOverscrollParams;
 }
 
 namespace content {
 class InputHandlerManager;
 
 class CONTENT_EXPORT InputHandlerManagerClient {
  public:
   virtual ~InputHandlerManagerClient() {}
 
   // Called from the main thread.
   virtual void SetInputHandlerManager(InputHandlerManager*) = 0;
   virtual void NotifyInputEventHandled(int routing_id,
                                        blink::WebInputEvent::Type type,
                                        InputEventAckState ack_result) = 0;
   virtual void ProcessRafAlignedInput(int routing_id) = 0;
 
   // Called from the compositor thread.
   virtual void RegisterRoutingID(int routing_id) = 0;
   virtual void UnregisterRoutingID(int routing_id) = 0;
+
+  // Fired when the overscroll was NOT caused by InputEvent.
+  // InputEvent associated overscroll will be returned along with the callback.

[dtapuska, 2016/08/30 18:33:50]

Likely should reference what callback you are indicating here that it it is part
of the HandleInputEvent method args.

[chongz, 2016/08/30 19:47:04]

Done.

   virtual void DidOverscroll(int routing_id,
                              const ui::DidOverscrollParams& params) = 0;
   virtual void DidStartFlinging(int routing_id) = 0;
   virtual void DidStopFlinging(int routing_id) = 0;
 
  protected:
   InputHandlerManagerClient() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InputHandlerManagerClient);
@@ skipping 11 matching lines @@
  protected:
   SynchronousInputHandlerProxyClient() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SynchronousInputHandlerProxyClient);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_INPUT_INPUT_HANDLER_MANAGER_CLIENT_H_