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

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 310e7b4f9fc12b3abfa57ef8090704e531d47d61..fd890e5d29bc6462ae7ca7fafb04cf64107fcffa 100644
--- a/content/common/presentation/presentation_service.mojom
+++ b/content/common/presentation/presentation_service.mojom
@@ -73,13 +73,12 @@ interface PresentationService {
   // 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