Added plumbing for the availablechange event from Blink to WebPresentationClient.

Source/modules/presentation/Presentation.h

 // Copyright 2014 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 Presentation_h
 #define Presentation_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "core/dom/ContextLifecycleObserver.h"
 #include "core/events/EventTarget.h"
 #include "modules/presentation/PresentationSession.h"
 
 namespace blink {
 
+class PresentationController;
 class ScriptState;
 
 class Presentation final
     : public RefCountedGarbageCollectedEventTargetWithInlineData<Presentation>
     , public ContextLifecycleObserver {
     DEFINE_EVENT_TARGET_REFCOUNTING_WILL_BE_REMOVED(RefCountedGarbageCollected<Presentation>);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Presentation);
     DEFINE_WRAPPERTYPEINFO();
 public:
     static Presentation* create(ExecutionContext*);
     virtual ~Presentation();
 
     // EventTarget implementation.
     virtual const AtomicString& interfaceName() const override;
     virtual ExecutionContext* executionContext() const override;
 
     virtual void trace(Visitor*) override;
 
     PresentationSession* session() const;
 
     ScriptPromise startSession(ScriptState*, const String& senderId, const String& presentationId);
     ScriptPromise joinSession(ScriptState*, const String& senderId, const String& presentationId);
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(availablechange);
 
+    virtual bool addEventListener(const AtomicString&, PassRefPtr<EventListener>, bool) override;

[Peter Beverloo, 2015/01/07 14:29:09]

Please give the "AtomicString" and "bool" arguments a name, as it's not obvious
what they mean.

[whywhat, 2015/01/07 16:22:16]

Done.

+    virtual bool removeEventListener(const AtomicString&, PassRefPtr<EventListener>, bool) override;
+
+    void deviceAvailabilityChanged(bool available);
 private:
     explicit Presentation(ExecutionContext*);
 
+    PresentationController* presentationController();
+    LocalFrame* frame();
+
     Member<PresentationSession> m_session;
 };
 
 } // namespace blink
 
 #endif // Presentation_h