[Presentation API] Change ListenForSessionMessages API to client-style.

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 18cb24c902f5ab9392fd2bf6735a63fbb34ca410..52a6c9ec1ae6cc2439a2c41ed9acf7f91f32ea97 100644
--- a/content/common/presentation/presentation_service.mojom
+++ b/content/common/presentation/presentation_service.mojom
@@ -33,8 +33,6 @@ enum PresentationMessageType {
 };
 
 struct SessionMessage {
-  string presentation_url;
-  string presentation_id;
   PresentationMessageType type;
   // Used when message type is TEXT.
   string? message;
@@ -90,7 +88,7 @@ interface PresentationService {
   // The false in the result callback notifies the renderer to stop sending
   // the send requests and invalidate all pending requests. This occurs
   // for eg., when frame is deleted or navigated away.
-  SendSessionMessage(SessionMessage message_request) => (bool success);
+  SendSessionMessage(PresentationSessionInfo sessionInfo, SessionMessage message_request) => (bool success);
 
   // Called when closeSession() is called by the frame.
   CloseSession(string presentation_url, string presentation_id);
@@ -100,11 +98,10 @@ interface PresentationService {
   // will be invoked with the session and its new state.
   ListenForSessionStateChange();
 
-  // Called when the frame is ready to process the next batch of messages.
-  // When the callback carries null messages, there is an error
-  // at the presentation service side.
-  ListenForSessionMessages()
-      => (array<SessionMessage>? messages);
+  // Starts listening for messages for session with |sessionInfo|.
+  // Messages will be received in
+  // PresentationServiceClient::OnSessionMessagesReceived.
+  ListenForSessionMessages(PresentationSessionInfo sessionInfo);

[haibinlu, 2015/07/30 23:16:30]

when will this be called? After api client attaches onmessage handler? If so,
shall there be also StopListen...?

[imcheng, 2015/08/03 18:56:33]

This is called after session is created which is the same as current behavior.
Blink changes are required to only call this when an event handler is attached,
in which case it will make sense to add a StopListen, similar to
ScreenAvailability.

 };
 
 interface PresentationServiceClient {
@@ -123,4 +120,7 @@ interface PresentationServiceClient {
   // See PresentationService::ListenForSessionStateChange.
   OnSessionStateChanged(PresentationSessionInfo sessionInfo,
                         PresentationSessionState newState);
+
+  // See PresentationService::ListenForSessionMessages.
+  OnSessionMessagesReceived(PresentationSessionInfo sessionInfo, array<SessionMessage> messages);
 };