[Presentation API] 1-UA presentation support + presenter APIs.

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 e201791642a0fc5ccf4128ecf03dff3e1d27e365..dd460538c3c633477de8c67d3bbad8e98c96cea9 100644
--- a/content/common/presentation/presentation_service.mojom
+++ b/content/common/presentation/presentation_service.mojom
@@ -104,6 +104,14 @@ interface PresentationService {
   // PresentationServiceClient::OnSessionMessagesReceived.
   // This is called after a presentation session is created.
   ListenForSessionMessages(PresentationSessionInfo sessionInfo);
+
+  // Gets a single receiver PresentationSessionInfo object for the
+  // offscreen presentation hosted on this frame.
+  // If the calling frame is not an offscreen presentation receiver frame,
+  // null will be returned.
+  // Otherwise, a receiver PresentationSessionInfo object will be returned,
+  // with url set to empty, and id set to the Id of the offscreen presentation.
+  GetPresentationReceiverSession() => (PresentationSessionInfo? session_info);
 };
 
 interface PresentationServiceClient {