Presentation API: ignore presentation id passed to startSession().

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 55 matching lines @@
   // session. If the default session is started by the embedder before this
   // call, the embedder may queue it and run the callback when the call is
   // performed.
   ListenForDefaultSessionStart()
       => (PresentationSessionInfo? defaultSessionInfo);
 
   // 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
   // session failed.
-  // The presentation id is always returned along with the initialized
-  // session on success.
-  // If the UA identifies a matching session (same presentation url and id),
-  // the user may choose this existing session and the page will join it
-  // rather than get a new one. An empty presentation id means that the
-  // UA will generate the presentation id.
-  StartSession(string presentation_url, string? presentation_id)
+  // The presentation id returned in |sessionInfo| on success is generated by
+  // the UA.
+  // If the UA identifies a matching session (same presentation url), the user
+  // may choose this existing session and the page will join it rather than get
+  // a new one.
+  StartSession(string presentation_url)
       => (PresentationSessionInfo? sessionInfo, PresentationError? error);
 
   // Called when joinSession() is called by the frame. The result callback
   // works the same as for the method above. JoinSession will join a known
   // session (i.e. when the page navigates or the user opens another tab)
   // silently and without user action.
   JoinSession(string presentation_url, string? presentation_id)
       => (PresentationSessionInfo? sessionInfo, PresentationError? error);
 
   // Called when send() is called by the frame. The true in the
@@ skipping 28 matching lines @@
   // Called when the client is listening for screen availability 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(bool available);
 
   // See PresentationService::ListenForSessionStateChange.
   OnSessionStateChanged(PresentationSessionInfo sessionInfo,
                         PresentationSessionState newState);
 };