Added plumbing for the availablechange event from Blink to WebPresentationClient.

Source/modules/presentation/AvailableChangeEvent.cpp

+// 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 "config.h"
+#include "modules/presentation/AvailableChangeEvent.h"
+
+namespace blink {
+
+AvailableChangeEvent::~AvailableChangeEvent()
+{
+}
+
+AvailableChangeEvent::AvailableChangeEvent()
+    : m_available(false)
+{
+}
+
+AvailableChangeEvent::AvailableChangeEvent(const AtomicString& eventType, bool available)
+    : Event(eventType, false, false)
+    , m_available(available)
+{
+}
+
+AvailableChangeEvent::AvailableChangeEvent(const AtomicString& eventType, const AvailableChangeEventInit& initializer)
+    : Event(eventType, initializer)
+    , m_available(initializer.available())
+{
+}
+
+const AtomicString& AvailableChangeEvent::interfaceName() const
+{
+    return EventNames::AvailableChangeEvent;
+}
+
+} // namespace blink