Teach input_handler_proxy about once callbacks.

ui/events/blink/event_with_callback.h

 // Copyright 2016 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_EVENT_WITH_CALLBACK_H_
 #define UI_EVENTS_BLINK_EVENT_WITH_CALLBACK_H_
 
 #include <list>
 
 #include "ui/events/blink/input_handler_proxy.h"
 #include "ui/latency/latency_info.h"
 
 namespace ui {
 
 namespace test {
 class InputHandlerProxyEventQueueTest;
 }
 
 class EventWithCallback {
  public:
   struct OriginalEventWithCallback {
     OriginalEventWithCallback(
         WebScopedInputEvent event,
-        const InputHandlerProxy::EventDispositionCallback& callback);
+        InputHandlerProxy::EventDispositionCallback callback);
     ~OriginalEventWithCallback();
     WebScopedInputEvent event_;
     InputHandlerProxy::EventDispositionCallback callback_;
   };
   using OriginalEventList = std::list<OriginalEventWithCallback>;
 
-  EventWithCallback(
-      WebScopedInputEvent event,
-      const LatencyInfo& latency,
-      base::TimeTicks timestamp_now,
-      const InputHandlerProxy::EventDispositionCallback& callback);
+  EventWithCallback(WebScopedInputEvent event,
+                    const LatencyInfo& latency,
+                    base::TimeTicks timestamp_now,
+                    InputHandlerProxy::EventDispositionCallback callback);
   EventWithCallback(WebScopedInputEvent event,
                     const LatencyInfo& latency,
                     base::TimeTicks creation_timestamp,
                     base::TimeTicks last_coalesced_timestamp,
                     std::unique_ptr<OriginalEventList> original_events);
   ~EventWithCallback();
 
   bool CanCoalesceWith(const EventWithCallback& other) const WARN_UNUSED_RESULT;
   void CoalesceWith(EventWithCallback* other, base::TimeTicks timestamp_now);
 
@@ skipping 24 matching lines @@
   LatencyInfo latency_;
   OriginalEventList original_events_;
 
   base::TimeTicks creation_timestamp_;
   base::TimeTicks last_coalesced_timestamp_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_BLINK_EVENT_WITH_CALLBACK_H_