Also three fixes for drawing to offscreen layers in MSKPPlayer:
*Only play from last full redraw to next cmd
*Clear before full redraw
*Actually track current cmd in layer state.
Bug: skia:11900
Change-Id: I988afb61f96c8acb7e7554d65bfa6cd6020196c7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407460
Reviewed-by: Nathaniel Nifong <nifong@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
33ec611316