Make SkSurface_Gpu::getDevice return a SkBaseGpuDevice

Change-Id: Ib678324849a15204c910df3361d7fd061cae1bb8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/411900
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed