[Presentation API] Plumbing the |defaultpresentationstart| event from Blink to browser/Mojo.

content/common/presentation/presentation_service.mojom

Index: content/common/presentation/presentation_service.mojom
diff --git a/content/common/presentation/presentation_service.mojom b/content/common/presentation/presentation_service.mojom
index d1e4b07909b59f888cd7f09433da54fcdb0742c0..a004dda4f48ea3e4c41fa6345cd91e34ece2f326 100644
--- a/content/common/presentation/presentation_service.mojom
+++ b/content/common/presentation/presentation_service.mojom
@@ -39,6 +39,16 @@ interface PresentationService {
     // |availablechange| event.
     OnScreenAvailabilityListenerRemoved();
 
+    // Called when |ondefaultpresentationstarted| listener is added or the page
+    // is ready to listen to the next such event. Indicates the frame is ready
+    // to handle the default presentation started by the user agent.
+    WaitForDefaultPresentation()

[Peter Beverloo, 2015/03/03 21:40:40]

ListenToDefaultPresentation perhaps? Wait* in naming usually implies that the
call will block until whatever it waits for has completed.

[whywhat, 2015/03/05 20:26:14]

Done.

+        => (PresentationSessionInfo defaultSessionInfo);
+
+    // Called when the frame no longer listens to the
+    // |ondefaultpresentationstarted| event.
+    OnDefaultPresentationListenerRemoved();
+
     // Called when startSession() is called by the frame. The result callback
     // will return a non-null and valid PresentationSessionInfo if starting the
     // session succeeded, or null with a PresentationError if starting the