Refactor compositor event handling path to be callback-based

ui/events/blink/input_handler_proxy.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 UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 #define UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 
 #include <memory>
 
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "cc/input/input_handler.h"
 #include "third_party/WebKit/public/platform/WebGestureCurve.h"
 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #include "third_party/WebKit/public/web/WebActiveWheelFlingParameters.h"
 #include "ui/events/blink/input_scroll_elasticity_controller.h"
+#include "ui/events/blink/scoped_web_input_event.h"
 #include "ui/events/blink/synchronous_input_handler_proxy.h"
 
 namespace ui {
 
 namespace test {
 class InputHandlerProxyTest;
 }
 
 class InputHandlerProxyClient;
 class InputScrollElasticityController;
@@ skipping 20 matching lines @@
   }
 
   void set_smooth_scroll_enabled(bool value) { smooth_scroll_enabled_ = value; }
 
   enum EventDisposition {
     DID_HANDLE,
     DID_NOT_HANDLE,
     DID_HANDLE_NON_BLOCKING,
     DROP_EVENT
   };
-  EventDisposition HandleInputEventWithLatencyInfo(
-      const blink::WebInputEvent& event,
-      ui::LatencyInfo* latency_info);
+  using EventDispositionCallback =
+      base::Callback<void(EventDisposition,
+                          ScopedWebInputEvent WebInputEvent,
+                          const LatencyInfo&,
+                          std::unique_ptr<ui::DidOverscrollParams>)>;
+  void HandleInputEventWithLatencyInfo(
+      ScopedWebInputEvent event,
+      const LatencyInfo& latency_info,
+      const EventDispositionCallback& callback);
   EventDisposition HandleInputEvent(const blink::WebInputEvent& event);
 
   // cc::InputHandlerClient implementation.
   void WillShutdown() override;
   void Animate(base::TimeTicks time) override;
   void MainThreadHasStoppedFlinging() override;
   void ReconcileElasticOverscrollAndRootScroll() override;
   void UpdateRootLayerStateForSynchronousInputHandler(
       const gfx::ScrollOffset& total_scroll_offset,
       const gfx::ScrollOffset& max_scroll_offset,
@@ skipping 60 matching lines @@
   bool CancelCurrentFling();
 
   // Returns true if we actually had an active fling to cancel.
   bool CancelCurrentFlingWithoutNotifyingClient();
 
   // Request a frame of animation from the InputHandler or
   // SynchronousInputHandler. They can provide that by calling Animate().
   void RequestAnimation();
 
   // Used to send overscroll messages to the browser.
-  void HandleOverscroll(
-      const gfx::Point& causal_event_viewport_point,
-      const cc::InputHandlerScrollResult& scroll_result);
+  // |bundle_overscroll_params_with_ack| means overscroll message should be
+  // bundled with triggering event response, and won't fire |DidOverscroll|.
+  void HandleOverscroll(const gfx::Point& causal_event_viewport_point,
+                        const cc::InputHandlerScrollResult& scroll_result,
+                        bool bundle_overscroll_params_with_ack);
 
   // Whether to use a smooth scroll animation for this event.
   bool ShouldAnimate(bool has_precise_scroll_deltas) const;
 
   // Update the elastic overscroll controller with |gesture_event|.
   void HandleScrollElasticityOverscroll(
       const blink::WebGestureEvent& gesture_event,
       const cc::InputHandlerScrollResult& scroll_result);
 
   std::unique_ptr<blink::WebGestureCurve> fling_curve_;
@@ skipping 49 matching lines @@
   bool smooth_scroll_enabled_;
   bool uma_latency_reporting_enabled_;
 
   // The merged result of the last touch start with previous touch starts.
   // This value will get returned for subsequent TouchMove events to allow
   // passive events not to block scrolling.
   int32_t touch_start_result_;
 
   base::TimeTicks last_fling_animate_time_;
 
+  // Used to record overscroll notifications while an event is being
+  // dispatched.  If the event causes overscroll, the overscroll metadata can be
+  // bundled in the event ack, saving an IPC.  Note that we must continue
+  // supporting overscroll IPC notifications due to fling animation updates.
+  std::unique_ptr<DidOverscrollParams> current_overscroll_params_;
+
   DISALLOW_COPY_AND_ASSIGN(InputHandlerProxy);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_