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

content/common/presentation/presentation_service.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module presentation;
 
 struct PresentationSessionInfo {
   string url;
   string id;
 };
@@ skipping 86 matching lines @@
   // When state change occurs, PresentationServiceClient::OnSessionStateChanged
   // will be invoked with the session and its new state.
   // This is called after a presentation session is created.
   ListenForSessionStateChange(PresentationSessionInfo sessionInfo);
 
   // Starts listening for messages for session with |sessionInfo|.
   // Messages will be received in
   // PresentationServiceClient::OnSessionMessagesReceived.
   // This is called after a presentation session is created.
   ListenForSessionMessages(PresentationSessionInfo sessionInfo);
+
+  // Gets a single receiver PresentationSessionInfo object for the

[miu, 2015/10/07 21:51:47]

See my comment in presentation_service_delegate.h, re: what if a receiver never
becomes available?

[imcheng, 2015/10/10 04:39:43]

since all mojo callbacks have to be invoked before they are destroyed, null will
be returned just before this request becomes invalid. Added comments.

+  // offscreen presentation hosted on the offscreen tab containing this frame.
+  // If the calling frame is not the main frame of an offscreen tab,
+  // null will be returned.
+  // Otherwise, a 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 {
   // Called when the client tries to listen for screen availability changes for
   // presentation of |url| but it is not supported by the device or underlying
   // platform. This can also be called if the device is currently in a mode
   // where it can't do screen discoveries (eg. low battery).
   OnScreenAvailabilityNotSupported(string url);
 
   // Called when the client is listening for screen availability for
   // presentation of |url| and the state changes. When the client starts to
   // listen for screen availability, this method will always be called to give
   // the current known state. It will then be called to notify of state updates.
   OnScreenAvailabilityUpdated(string url, bool available);
 
   // See PresentationService::ListenForSessionStateChange.
   OnSessionStateChanged(PresentationSessionInfo sessionInfo,
                         PresentationSessionState newState);
 
   // See PresentationService::ListenForSessionMessages.
   OnSessionMessagesReceived(PresentationSessionInfo sessionInfo, array<SessionMessage> messages);
 };