Also adds a set_buffer method, as the only public setter for capacity_.
Bug: webrtc:9378
Change-Id: If0257c6d00bc8690f0428a3edc20b6da6dfa7119
Reviewed-on: https://webrtc-review.googlesource.com/c/112134
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25962}