This introduces AdaptationTargetOrReason and gets rid of
VideoStreamAdapter's dependency on the VideoStreamEncoderObserver.
AdaptationTargetOrReason provides information about why an adaptation
target could not be returned from GetAdaptUpTarget() and
GetAdaptDownTarget() with the enum CannotAdaptReason and the boolean
min_pixel_limit_reached.
While the enum value is not used by the caller in this CL, it makes
explicit reasons the adapter is allowed to reject a target. TODOs are
added documenting how we want to get rid of kAwaitingPreviousAdaptation
for multi-stream use cases and how kIsBitrateConstrained can be
rephrased as a resource problem in the future.
min_pixel_limit_reached() allows us to move the responsibility of stats
reporting to the module. A TODO documents how this could be replaced by
kLimitReached or similar logic in the future.
Bug: webrtc:11393
Change-Id: Iffdd8ddb01641937741fac353174ea14168477ce
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169928
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30789}
3453149b28