[Presentation API] Added the DefaultPresentationStart event and parsing of the default presentation…

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 ac5879ecae4052a942ff1faa58c77517130e186c..89846e7a5d750685e7ef5b143c3def65532d2b1b 100644
--- a/Source/modules/presentation/PresentationController.h
+++ b/Source/modules/presentation/PresentationController.h
@@ -15,6 +15,7 @@
 namespace blink {
 
 class LocalFrame;
+class WebPresentationSessionClient;
 
 // The coordinator between the various page exposed properties and the content
 // layer represented via |WebPresentationClient|.
@@ -41,6 +42,7 @@ public:
     // Implementation of WebPresentationController.
     virtual void didChangeAvailability(bool available) override;
     virtual bool isAvailableChangeWatched() const override;
+    virtual void didStartDefaultSession(WebPresentationSessionClient*) override;
 
     // Called when the first listener was added to or the last listener was removed from the
     // |availablechange| event.