Convert WaitableEvent::EventCallback to OnceCallback

base/synchronization/waitable_event_watcher_win.cc

Index: base/synchronization/waitable_event_watcher_win.cc
diff --git a/base/synchronization/waitable_event_watcher_win.cc b/base/synchronization/waitable_event_watcher_win.cc
index a3eb73b10e081cae2ab8f5d94a20ffd1d5a9226c..f3e114e3966149c610d5579ec69fddaf32555c5f 100644
--- a/base/synchronization/waitable_event_watcher_win.cc
+++ b/base/synchronization/waitable_event_watcher_win.cc
@@ -15,10 +15,9 @@ WaitableEventWatcher::WaitableEventWatcher() = default;
 WaitableEventWatcher::~WaitableEventWatcher() {
 }
 
-bool WaitableEventWatcher::StartWatching(
-    WaitableEvent* event,
-    const EventCallback& callback) {
-  callback_ = callback;
+bool WaitableEventWatcher::StartWatching(WaitableEvent* event,
+                                         EventCallback callback) {
+  callback_ = std::move(callback);
   event_ = event;
   return watcher_.StartWatchingOnce(event->handle(), this);
 }
@@ -31,12 +30,11 @@ void WaitableEventWatcher::StopWatching() {
 
 void WaitableEventWatcher::OnObjectSignaled(HANDLE h) {
   WaitableEvent* event = event_;
-  EventCallback callback = callback_;
+  EventCallback callback = std::move(callback_);
   event_ = NULL;
-  callback_.Reset();
   DCHECK(event);
 
-  callback.Run(event);
+  std::move(callback).Run(event);
 }
 
 }  // namespace base