Reason for revert:
This CL depends on a reverted CL.
Original issue's description:
> Add unit tests for RTCMTLVideoView.
>
> To properly test the functionality, following changes were needed
> - Make RTCMTLVideoView compiliable for all cpu architectures not just arm64.
> This is needed so that the test can run on any device and on simulator as well.
> - Refactor RTCMTLVideoView to have mockable class methods.
> The unittest class, RTCMTLVideoViewTests was designed to provide easy transition
> to XCTest when the time comes for that.
> To transition to XCTest it would suffice to inherit from XCTestCase and remove
> the gtest methods.
>
> BUG=webrtc:7079
>
> Review-Url: https://codereview.webrtc.org/2723903003
> Cr-Commit-Position: refs/heads/master@{#17014}
> Committed: 0ebe0199acTBR=magjed@webrtc.org,denicija@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7079
Review-Url: https://codereview.webrtc.org/2733953006
Cr-Commit-Position: refs/heads/master@{#17118}
96d91524fa