Don't use PostTask queueing between compositor and main thread.

content/common/input/event_with_latency_info.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_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_
 #define CONTENT_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "content/common/content_export.h"
+#include "content/common/input/scoped_web_input_event.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/events/latency_info.h"
 
 namespace content {
 namespace internal {
 
 bool CONTENT_EXPORT CanCoalesce(const blink::WebMouseEvent& event_to_coalesce,
                                 const blink::WebMouseEvent& event);
 void CONTENT_EXPORT Coalesce(const blink::WebMouseEvent& event_to_coalesce,
                              blink::WebMouseEvent* event);
 bool CONTENT_EXPORT
 CanCoalesce(const blink::WebMouseWheelEvent& event_to_coalesce,
             const blink::WebMouseWheelEvent& event);
 void CONTENT_EXPORT Coalesce(const blink::WebMouseWheelEvent& event_to_coalesce,
                              blink::WebMouseWheelEvent* event);
 bool CONTENT_EXPORT CanCoalesce(const blink::WebTouchEvent& event_to_coalesce,
                                 const blink::WebTouchEvent& event);
 void CONTENT_EXPORT Coalesce(const blink::WebTouchEvent& event_to_coalesce,
                              blink::WebTouchEvent* event);
 bool CONTENT_EXPORT CanCoalesce(const blink::WebGestureEvent& event_to_coalesce,
                                 const blink::WebGestureEvent& event);
 void CONTENT_EXPORT Coalesce(const blink::WebGestureEvent& event_to_coalesce,
                              blink::WebGestureEvent* event);
 
 }  // namespace internal
 
+class ScopedWebInputEventWithLatencyInfo {
+ public:
+  ScopedWebInputEventWithLatencyInfo(const blink::WebInputEvent& e,
+                                     const ui::LatencyInfo& l);
+
+  ~ScopedWebInputEventWithLatencyInfo();
+
+  bool CanCoalesceWith(const ScopedWebInputEventWithLatencyInfo& other) const
+      WARN_UNUSED_RESULT;
+
+  const blink::WebInputEvent& event() const;
+  blink::WebInputEvent& event();
+  const ui::LatencyInfo latencyInfo() const { return latency_; }
+
+  void CoalesceWith(const ScopedWebInputEventWithLatencyInfo& other);
+
+ private:
+  ScopedWebInputEvent event_;
+  mutable ui::LatencyInfo latency_;

[tdresser, 2016/07/20 20:52:27]

I don't feel great about this being mutable. It's needed for coalescing, right?
Could we just make the event being coalesced non-const?

+};
+
 template <typename T>
 class EventWithLatencyInfo {
  public:
   T event;
   mutable ui::LatencyInfo latency;
 
   explicit EventWithLatencyInfo(const T& e) : event(e) {}
 
   EventWithLatencyInfo(const T& e, const ui::LatencyInfo& l)
       : event(e), latency(l) {}
@@ skipping 35 matching lines @@
 typedef EventWithLatencyInfo<blink::WebMouseWheelEvent>
     MouseWheelEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebMouseEvent>
     MouseEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebTouchEvent>
     TouchEventWithLatencyInfo;
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_