Keep methods on subclasses where they are used: FifoBuffer and
MemoryStream. Also FileStream gets to keep SetPosition, because it's
used by a downstream subclass.
Bug: webrtc:6424
Change-Id: If2a00855aba7c2c9dc0909cda7c8a8ef00e0b9af
Reviewed-on: https://webrtc-review.googlesource.com/c/116487
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26237}