It makes sense to clean up self.videoFrame in -teardownGL, but if
we happen to have a frame available in -setupGL then it's OK to
keep using that frame. Clearing the frame here frequently causes
the screen view to go black for a moment when the app returns from
the background.
Bug: webrtc:10059
Change-Id: Ic62f872a0a582c807cee1e30ea9bb32f31ada341
Reviewed-on: https://webrtc-review.googlesource.com/c/112213
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25816}