Add a 'closeRenderTasksForNewOpList' method to GrDrawingManager

This consolidates some duplicate code across newRTOpList and
newTextureOpList.

Bug: skia:
Change-Id: I3a3c150e20e3db279de476307c5281668c3fdd9a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232836
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed