Sync ui/events to chromium @ https://codereview.chromium.org/1210203002

ui/events/null_event_targeter.h

+// Copyright 2015 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.
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "ui/events/event_targeter.h"
+#include "ui/events/events_export.h"
+
+namespace ui {
+
+// NullEventTargeter can be installed on a root window to prevent it from
+// dispatching events such as during shutdown.
+class EVENTS_EXPORT NullEventTargeter : public EventTargeter {
+ public:
+  NullEventTargeter();
+  ~NullEventTargeter() override;
+
+  // EventTargeter:
+  EventTarget* FindTargetForEvent(EventTarget* root, Event* event) override;
+  EventTarget* FindNextBestTarget(EventTarget* previous_target,
+                                  Event* event) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NullEventTargeter);
+};
+
+}  // namespace ui