Try to use frame timestamps first if they look reasonable, otherwise use realtime clock. Also, lower limit from 90% of target to 85%. Bug: webrtc:4172, chromium:802290 Change-Id: Iad489be7c7cf637345be4795e5089936ab9fab07 Reviewed-on: https://webrtc-review.googlesource.com/41041 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Cr-Commit-Position: refs/heads/master@{#21729}