Added plumbing for the availablechange event from Blink to WebPresentationClient.

Source/modules/presentation/AvailableChangeEvent.cpp

Index: Source/modules/presentation/AvailableChangeEvent.cpp
diff --git a/Source/modules/presentation/AvailableChangeEvent.cpp b/Source/modules/presentation/AvailableChangeEvent.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..781ccefdeb7183e499549e1fc21877d4aa1819ec
--- /dev/null
+++ b/Source/modules/presentation/AvailableChangeEvent.cpp
@@ -0,0 +1,36 @@
+// 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