Fix tests in WebRtcVideoChannelBaseTest.
Fix tests in WebRtcVideoChannelBaseTest.

If rtc_libvpx_build_vp9=false, some tests fail because
BuiltinVideoEncoderFactory / DecoderFactory doesn't support VP9.

Bug: webrtc:11901
Change-Id: Iaa97950e70e1f70cdeb6ef677786e0fd115a75db
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183220
Reviewed-by: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Commit-Queue: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#32028}

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