Added plumbing for the availablechange event from Blink to WebPresentationClient.

Source/modules/presentation/AvailableChangeEvent.h

Index: Source/modules/presentation/AvailableChangeEvent.h
diff --git a/Source/modules/presentation/AvailableChangeEvent.h b/Source/modules/presentation/AvailableChangeEvent.h
new file mode 100644
index 0000000000000000000000000000000000000000..bb57b942605b501310c14e245ef127beac6bcb72
--- /dev/null
+++ b/Source/modules/presentation/AvailableChangeEvent.h
@@ -0,0 +1,50 @@
+// 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.
+
+#ifndef AvailableChangeEvent_h
+#define AvailableChangeEvent_h
+
+#include "modules/EventModules.h"
+#include "modules/presentation/AvailableChangeEventInit.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+// AvailableChangeEvent object definition corresponding to the event IDL from the Presentation API,
+// see https://w3c.github.io/presentation-api/#availablechangeevent for details.
+class AvailableChangeEvent final : public Event {
+    DEFINE_WRAPPERTYPEINFO();
+public:
+    virtual ~AvailableChangeEvent();
+
+    static PassRefPtrWillBeRawPtr<AvailableChangeEvent> create()
+    {
+        return adoptRefWillBeNoop(new AvailableChangeEvent);
+    }
+    static PassRefPtrWillBeRawPtr<AvailableChangeEvent> create(const AtomicString& eventType, bool available)
+    {
+        return adoptRefWillBeNoop(new AvailableChangeEvent(eventType, available));
+    }
+    static PassRefPtrWillBeRawPtr<AvailableChangeEvent> create(const AtomicString& eventType, const AvailableChangeEventInit& initializer)
+    {
+        return adoptRefWillBeNoop(new AvailableChangeEvent(eventType, initializer));
+    }
+
+    bool available() const { return m_available; }
+
+    virtual const AtomicString& interfaceName() const override;
+
+private:
+    AvailableChangeEvent();
+    AvailableChangeEvent(const AtomicString& eventType, bool available);
+    AvailableChangeEvent(const AtomicString& eventType, const AvailableChangeEventInit& initializer);
+
+    bool m_available;
+};
+
+DEFINE_TYPE_CASTS(AvailableChangeEvent, Event, event, event->interfaceName() == EventNames::AvailableChangeEvent, event.interfaceName() == EventNames::AvailableChangeEvent);
+
+} // namespace blink
+
+#endif // AvailableChangeEvent_h