[PresentationAPI] Added on-session-message handler.

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;
 };
 
 enum PresentationSessionState {
     CONNECTED,
     DISCONNECTED
 };
 
 enum PresentationErrorType {
     NO_AVAILABLE_SCREENS,
     SESSION_REQUEST_CANCELLED,
     NO_PRESENTATION_FOUND,
     UNKNOWN,
 };
 
 struct PresentationError {
     PresentationErrorType error_type;
     string message;
 };
 
+enum PresentationMessageType {
+   TEXT,
+   ARRAY_BUFFER,
+};
+
+struct SessionMessage {
+   string presentation_url;
+   string presentation_id;
+   PresentationMessageType type;
+   string? message;
+   array<uint8>? data;
+};
+
 interface PresentationService {
     // Called when the frame sets or changes the default presentation URL or
     // presentation ID.
     SetDefaultPresentationURL(
         string default_presentation_url,
         string? default_presentation_id);
 
     // Returns the last screen availability state if it’s changed since the last
     // time the method was called. The client has to call this method again when
     // handling the result (provided via Mojo callback) to get the next update
@@ skipping 37 matching lines @@
 
     // Called when closeSession() is called by the frame.
     CloseSession(string presentation_url, string presentation_id);
 
     // Called when the frame is ready to process the next state change. Returns
     // the last session state if it’s changed since the last time the callback
     // was called. Might cause the event fired with the initial state change.
     ListenForSessionStateChange()
         => (PresentationSessionInfo sessionInfo,
             PresentationSessionState newState);
+
+    // Called when the frame is ready to process the next batch of messages.
+    ListenForSessionMessages()
+        => (array<SessionMessage> messages);
 };