Update mock render task & cluster test

Switch away from views, and add support for simulating
used-proxies. The latter will be used in an upcoming CL.

Bug: skia:10877
Change-Id: I7897516dc53c075a286cce8f31075d8cc93abccf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/360604
Commit-Queue: Robert Phillips <robertphillips@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed