This introduces a new class for encapsulating the QualityRampupExperiment R=hbos@webrtc.org Bug: webrtc:11553 Change-Id: If2f2347cdcbd0c79821355f90e2d7ad3171143b5 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176363 Commit-Queue: Evan Shrubsole <eshr@google.com> Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/master@{#31531}