[Presentation API] Adds close method to Presentation session.

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 89846e7a5d750685e7ef5b143c3def65532d2b1b..ad2aae3386e3239ccdf4e660fdaad53430e39970 100644
--- a/Source/modules/presentation/PresentationController.h
+++ b/Source/modules/presentation/PresentationController.h
@@ -54,6 +54,9 @@ public:
     // Called when the frame wants to join an existing presentation.
     void joinSession(const String& presentationUrl, const String& presentationId, WebPresentationSessionClientCallbacks*);
 
+    // Called when the frame wants to close an existing presentation.
+    void closeSession(const String& url, const String& presentationId);
+
     // Connects the |Presentation| object with this controller.
     void setPresentation(Presentation*);