[PresentationAPI] Added plumbing for start/joinSession from JS to platform

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/events/EventTarget.h"
 #include "core/frame/DOMWindowProperty.h"
 #include "modules/presentation/PresentationSession.h"
 #include "platform/heap/Handle.h"
+#include "platform/heap/Heap.h"
 
 namespace WTF {
 class String;
 } // namespace WTF
 
 namespace blink {
 
 class LocalFrame;
 class PresentationController;
 class ScriptState;
@@ skipping 26 matching lines @@
     // 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;
+    // Adds a session to the open sessions list.
+    void didCreateSession(PresentationSession*);
+
 private:
     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();
 
+    // The session object provided to the presentation page. Not supported.
     Member<PresentationSession> m_session;
+
+    // The sessions opened for this frame.
+    HeapHashSet<Member<PresentationSession>> m_openSessions;
 };
 
 } // namespace blink
 
 #endif // Presentation_h