This setter method is intended to replace all direct assignments to
the |_size| member. A later cl will make that member private, and
rename it to |capacity_|.
Bug: webrtc:9378
Change-Id: I37e9eb54d1c72bcd4cb8a1cfef34bbc6c209bd0d
Reviewed-on: https://webrtc-review.googlesource.com/c/113060
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25894}