Call GrContext::performDeferredCleanup from viewer

Bug: skia:
Change-Id: I723c5efdd746d6182dee0511795f7eca3b6066d3
Reviewed-on: https://skia-review.googlesource.com/c/167180
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
3 files changed