[Blink, RemotePlayback] watchAvailability() implementation.

third_party/WebKit/Source/modules/remoteplayback/RemotePlaybackAvailability.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 RemotePlaybackAvailability_h
-#define RemotePlaybackAvailability_h
-
-#include "bindings/core/v8/ActiveScriptWrappable.h"
-#include "core/dom/ContextLifecycleObserver.h"
-#include "core/events/EventTarget.h"
-
-namespace blink {
-
-class ExecutionContext;
-class ScriptPromiseResolver;
-
-// Expose whether there is a remote playback device available for a media
-// element. The object will be initialized with a default value passed via
-// ::take() and will then listen to availability changes.
-class RemotePlaybackAvailability final : public EventTargetWithInlineData,
-                                         public ActiveScriptWrappable,
-                                         public ContextLifecycleObserver {
-  DEFINE_WRAPPERTYPEINFO();
-  USING_GARBAGE_COLLECTED_MIXIN(RemotePlaybackAvailability);
-
- public:
-  static RemotePlaybackAvailability* take(ScriptPromiseResolver*, bool);
-  ~RemotePlaybackAvailability() override;
-
-  // EventTarget implementation.
-  const AtomicString& interfaceName() const override;
-  ExecutionContext* getExecutionContext() const override;
-
-  void availabilityChanged(bool);
-
-  bool value() const;
-
-  // ScriptWrappable implementation.
-  bool hasPendingActivity() const final;
-
-  DEFINE_ATTRIBUTE_EVENT_LISTENER(change);
-
-  DECLARE_VIRTUAL_TRACE();
-
- private:
-  RemotePlaybackAvailability(ExecutionContext*, bool);
-
-  bool m_value;
-};
-
-}  // namespace blink
-
-#endif  // RemotePlaybackAvailability_h