[graphite] Hook up viewer

Bug: skia:12633
Change-Id: Id0bd892375e3a3e2886714f19b7fd8da2232e4e2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/479736
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
6 files changed