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

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 1d4c7b957f4eb477d75b03f0c8345a060c526876..ac5879ecae4052a942ff1faa58c77517130e186c 100644
--- a/Source/modules/presentation/PresentationController.h
+++ b/Source/modules/presentation/PresentationController.h
@@ -9,12 +9,12 @@
 #include "modules/presentation/Presentation.h"
 #include "platform/Supplementable.h"
 #include "platform/heap/Handle.h"
+#include "public/platform/modules/presentation/WebPresentationClient.h"
 #include "public/platform/modules/presentation/WebPresentationController.h"
 
 namespace blink {
 
 class LocalFrame;
-class WebPresentationClient;
 
 // The coordinator between the various page exposed properties and the content
 // layer represented via |WebPresentationClient|.
@@ -46,6 +46,12 @@ public:
     // |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*);
+
+    // Called when the frame wants to join an existing presentation.
+    void joinSession(const String& presentationUrl, const String& presentationId, WebPresentationSessionClientCallbacks*);
+
     // Connects the |Presentation| object with this controller.
     void setPresentation(Presentation*);