Fix an likely ClassCastException in Notification.visitUris

The code (and unit test) treated EXTRA_AUDIO_CONTENTS_URI as a Uri, but the extra is very explicitly documented as a String.  Sample code and everything.

Fixes: 182997213
Test: atest NotificationManagerServiceTest#testVisitUris
Test: atest NotificationManagerServiceTest#testVisitUris_audioContentsString
Change-Id: I3cfc657f88d8e273270c777b199ce056ff2ffc67
2 files changed