Presentation API: implement .getAvalability() (Blink side).

Source/modules/presentation/PresentationController.h

Index: Source/modules/presentation/PresentationController.h
diff --git a/Source/modules/presentation/PresentationController.h b/Source/modules/presentation/PresentationController.h
index 3b1ea1f74da7deefaba029a0500fc3c56a1f2261..39e4fd12dbfd4ea2c018e51c881224f26cfbf240 100644
--- a/Source/modules/presentation/PresentationController.h
+++ b/Source/modules/presentation/PresentationController.h
@@ -16,6 +16,7 @@
 namespace blink {
 
 class LocalFrame;
+class WebPresentationAvailabilityCallback;
 class WebPresentationSessionClient;
 enum class WebPresentationSessionState;
 
@@ -38,6 +39,8 @@ public:
 
     static void provideTo(LocalFrame&, WebPresentationClient*);
 
+    WebPresentationClient* client();

[whywhat, 2015/07/02 22:32:38]

I think this is inconsistent with the other methods and breaks the encapsulation
of the controller somewhat although makes the plumbing a bit easier.
To remain consistent there should be start/stopListening() methods in the
controller to pass the observer to the client.

[mlamouri (slow - plz ping), 2015/07/03 13:58:26]

The only reason why these controllers exist is to hold the FooClient that can't
be accessed from inside a module otherwise. I think these controllers should
limit themselves to this purpose: make sure m_client is never stall. This is
what the PermissionController is doing for example. It's a simple class with a
simple purpose. I think the boilerplate added by having the Controller being
used to make calls is unecessary.

In the long term, the Client should be available by other means than using a
Controller. I sent a Design Doc a while ago to blink-dev with an idea.
Unfortunately, I didn't found the time to go forward with the idea but I think
reducing Controller role is the way forward.

+
     // Implementation of HeapSupplement.
     DECLARE_VIRTUAL_TRACE();
 
@@ -48,10 +51,6 @@ public:
     virtual void didChangeSessionState(WebPresentationSessionClient*, WebPresentationSessionState) override;
     virtual void didReceiveSessionTextMessage(WebPresentationSessionClient*, const WebString&) override;
 
-    // Called when the first listener was added to or the last listener was removed from the
-    // |availablechange| event.
-    void updateAvailableChangeWatched(bool watched);
-
     // Called when the frame wants to start a new presentation.
     void startSession(const String& presentationUrl, const String& presentationId, WebPresentationSessionClientCallbacks*);
 
@@ -70,6 +69,9 @@ public:
     // Called when the frame wants to close an existing presentation.
     void closeSession(const String& url, const String& presentationId);
 
+    // Called when the frame wants to know the availability of a device to present.
+    void getAvailability(const String& presentationUrl, WebPresentationAvailabilityCallbacks*);
+
     // Connects the |Presentation| object with this controller.
     void setPresentation(Presentation*);