If minQP is reached and encoder undershoot consistently, we consider the quality good enough and throttle encode frame rate. This CL also adds perf tests for high fps vp9 screenshare. Bug: webrtc:10310 Change-Id: I49fc7d31f9f596a9ecb5f85fe9e0c7861d4915f9 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/125761 Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/master@{#26997}