DependencyDescriptor and vp9 wrapper understand key frame differently
when it comes to the first layer frame with spatial_id>0
This CL adds and use DD's interpretation of the key frame when deciding
if DD should be supported going forward.
Bug: webrtc:11999
Change-Id: I11a809a315e18bd856bb391576c6ea1f427e33be
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/202760
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33046}