Add UseCounters for ViewportAPI

third_party/WebKit/Source/core/events/VisualViewportScrollEvent.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 VisualViewportScrollEvent_h
+#define VisualViewportScrollEvent_h
+
+#include "core/events/Event.h"
+
+namespace blink {
+
+class VisualViewportScrollEvent final : public Event {
+public:
+    ~VisualViewportScrollEvent() override;
+
+    static VisualViewportScrollEvent* create()
+    {
+        return new VisualViewportScrollEvent();
+    }
+
+    void doneDispatchingEventAtCurrentTarget() override;
+
+    DEFINE_INLINE_VIRTUAL_TRACE() { Event::trace(visitor); }
+
+private:
+    VisualViewportScrollEvent();
+};
+
+} // namespace blink
+
+#endif // VisualViewportScrollEvent_h