This CL takes us one step closer to being able to evaluate alternative
possible adaptation targets (e.g. multi-stream adaptation) by exposing
the target separately from applying it.
This is a refactoring of OnResourceUnderuse() and OnResourceOveruse().
Prior to this CL, the target resolution or frame rate was calculated
inside these methods and applied if possible. This CLs makes these two
steps (calculating a usable target + applying it) separate methods.
After this CL, the target is expressed as AdaptationTarget and is
calculated and returned by GetAdaptUpTarget() and GetAdaptDownTarget().
The target is only returned if it can be applied - and CanAdaptUp() +
CanAdaptDown() are merged with these methods.
Applying the target happens at ApplyAdaptationTarget().
Bug: webrtc:11222
Change-Id: I8e488be1d1590c23848db816d49a7738562e176d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169100
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30643}
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