Expose OpusTest class for re-use as chromium test.
Expose OpusTest class for re-use as chromium test.

This CL allows to trigger related tests when rolling opus
(at chromium side).

Bug: chromium:1002973
Change-Id: I811d17233367cabc8b4aa8ab5bbf3e92359afbce
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158887
Commit-Queue: Yves Gerey <0554266f02d7ad5bb902ac47b1c8525c05c3857c@google.com>
Reviewed-by: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29716}

TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc