This creates a funnel in the drawing manager (removeRenderTasks) that
opens the door for tighter integration between the two classes. Also we
add some assertions about the relationship and cut out duplicated code.
Bug: skia:10372
Change-Id: I0781ba7d45ac090cf7f6d430f0d56afe0f98b7e0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297195
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>