Yet more GrThreadSafeUniquelyKeyedProxyViewCache purging tests

This CL also renames dropAllUniqueRefs

Bug: 1108408
Change-Id: Ic39ccfc5efafd60d53524562dd308102fb134d94
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/318737
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed