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 "core/frame/FrameDestructionObserver.h"
 #include "modules/presentation/PresentationSession.h"
 
 namespace blink {
 
+class LocalFrame;
+class PresentationController;
 class ScriptState;
 
+// Implements the main entry point of the Presentation API corresponding to the Presentation.idl
+// See https://w3c.github.io/presentation-api/#navigatorpresentation for details.
 class Presentation final
     : public RefCountedGarbageCollectedEventTargetWithInlineData<Presentation>
-    , public ContextLifecycleObserver {
+    , public FrameDestructionObserver {
     DEFINE_EVENT_TARGET_REFCOUNTING_WILL_BE_REMOVED(RefCountedGarbageCollected<Presentation>);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Presentation);
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static Presentation* create(ExecutionContext*);
+    static Presentation* create(LocalFrame*);
     virtual ~Presentation();
 
     // EventTarget implementation.
     virtual const AtomicString& interfaceName() const override;

[mark a. foltz, 2015/01/26 19:53:38]

Do AtomicString, String, ExecutionContext, Visitor, etc. need to be forward
declared?

[whywhat, 2015/01/27 13:51:24]

I don't usually forward declare types required in overridden methods - it must
be done in the base class header.
So from those listed, String is the only one that needs a forward declaration
from my point of view (though all of them are included through others somehow it
seems).

     virtual ExecutionContext* executionContext() const override;
 
     virtual void trace(Visitor*) override;
 
     PresentationSession* session() const;
 
     ScriptPromise startSession(ScriptState*, const String& senderId, const String& presentationId);

[mark a. foltz, 2015/01/26 19:53:38]

Which parameter conveys the presented URL?  Should senderId be named
presentationUrl?

[whywhat, 2015/01/27 13:51:24]

Yes, a copy/paste error from some old API reference page probably...

     ScriptPromise joinSession(ScriptState*, const String& senderId, const String& presentationId);

[mark a. foltz, 2015/01/26 19:53:38]

Ditto

[whywhat, 2015/01/27 13:51:24]

Done.

 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(availablechange);
 
+    // The embedder needs to keep track if anything is listening to the event so it could stop the
+    // might be expensive screen discovery process.
+    virtual bool addEventListener(const AtomicString& eventType, PassRefPtr<EventListener>, bool useCapture) override;
+    virtual bool removeEventListener(const AtomicString& eventType, PassRefPtr<EventListener>, bool useCapture) override;
+    virtual void removeAllEventListeners() override;
+
+    // Called when the |availablechange| event needs to be fired.
+    void didChangeAvailability(bool available);
+    // Queried by the controller if |availablechange| event has any listeners.
+    bool isAvailableChangeWatched() const;
 private:
-    explicit Presentation(ExecutionContext*);
+    explicit Presentation(LocalFrame*);
+
+    // Returns the |PresentationController| object associated with the frame |Presentation| corresponds to.
+    // Can return |nullptr| if the frame is detached from the document.
+    PresentationController* presentationController();
 
     Member<PresentationSession> m_session;
 };
 
 } // namespace blink
 
 #endif // Presentation_h