Teach input_handler_proxy about once callbacks.

ui/events/blink/event_with_callback.h

Index: ui/events/blink/event_with_callback.h
diff --git a/ui/events/blink/event_with_callback.h b/ui/events/blink/event_with_callback.h
index f56c63db45860d0e2ad278940622953bc9b475e8..774b8e86de489ffafc0a2f143db90a2cb4160a46 100644
--- a/ui/events/blink/event_with_callback.h
+++ b/ui/events/blink/event_with_callback.h
@@ -21,18 +21,17 @@ class EventWithCallback {
   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,