Minor refactoring of the AudioDeviceBuffer class

BUG=NONE
NOTRY=true

Review-Url: https://codereview.webrtc.org/2117303002
Cr-Original-Commit-Position: refs/heads/master@{#13389}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3f33e2aa54565e1bf81caec5db4e4b910cf504c1
2 files changed