Added plumbing for the availablechange event from Blink to WebPresentationClient.

Source/modules/presentation/Presentation.h

Index: Source/modules/presentation/Presentation.h
diff --git a/Source/modules/presentation/Presentation.h b/Source/modules/presentation/Presentation.h
index f075f735defa029934d85005b0dfbde8dcd4e0ec..5f88514b509d85545ea24c956412fb08196c60e1 100644
--- a/Source/modules/presentation/Presentation.h
+++ b/Source/modules/presentation/Presentation.h
@@ -12,6 +12,7 @@
 
 namespace blink {
 
+class PresentationController;
 class ScriptState;
 
 class Presentation final
@@ -37,9 +38,17 @@ public:
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(availablechange);
 
+    // The UA needs to keep track if anything is listening to the event so it could stop the might

[Peter Beverloo, 2015/01/07 19:53:11]

s/UA/embedder/

[whywhat, 2015/01/08 16:05:28]

Done.

+    // 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;
+
+    void didChangeAvailability(bool available);
 private:
     explicit Presentation(ExecutionContext*);
 
+    PresentationController* presentationController();
+
     Member<PresentationSession> m_session;
 };