Add UseCounters for ViewportAPI

third_party/WebKit/Source/core/events/VisualViewportScrollEvent.cpp

Index: third_party/WebKit/Source/core/events/VisualViewportScrollEvent.cpp
diff --git a/third_party/WebKit/Source/core/events/VisualViewportScrollEvent.cpp b/third_party/WebKit/Source/core/events/VisualViewportScrollEvent.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..cb297d100c134f57f8a5204c4e6956a083ab7ed9
--- /dev/null
+++ b/third_party/WebKit/Source/core/events/VisualViewportScrollEvent.cpp
@@ -0,0 +1,29 @@
+// 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.
+
+#include "core/events/VisualViewportScrollEvent.h"
+
+#include "core/frame/UseCounter.h"
+
+namespace blink {
+
+VisualViewportScrollEvent::~VisualViewportScrollEvent()
+{
+}
+
+VisualViewportScrollEvent::VisualViewportScrollEvent()
+    : Event(EventTypeNames::scroll, false, false) // non-bubbling non-cancellable
+{
+}
+
+void VisualViewportScrollEvent::doneDispatchingEventAtCurrentTarget()
+{
+    UseCounter::count(currentTarget()->getExecutionContext(),
+        UseCounter::VisualViewportScrollFired);
+}
+
+} // namespace blink
+
+
+