Reland "Make GrVkBackendContext no longer derive from SkRefCnt."

This reverts commit 059a9ab4bcd07a4bfdbfef333c27ef3d277e0e46.

Reason for revert: Fix landed in Fuchsia

Original change's description:
> Revert "Make GrVkBackendContext no longer derive from SkRefCnt."
> 
> This reverts commit 93ae2337732bf206e6ef4faecc6b30c3881e8359.
> 
> Reason for revert: <INSERT REASONING HERE>
> 
> Original change's description:
> > Make GrVkBackendContext no longer derive from SkRefCnt.
> > 
> > Also moves the helper Create functions to VkTestUtils since no clients
> > are using them anymore.
> > 
> > Bug: skia:
> > Change-Id: I7e8e4912e7ef6fb00a7e2a00407aed5e83211799
> > Reviewed-on: https://skia-review.googlesource.com/135323
> > Reviewed-by: Jim Van Verth <jvanverth@google.com>
> > Reviewed-by: Brian Salomon <bsalomon@google.com>
> > Commit-Queue: Greg Daniel <egdaniel@google.com>
> 
> TBR=egdaniel@google.com,jvanverth@google.com,bsalomon@google.com
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Bug: skia:
> Change-Id: If7201917631dc22753ea3fa6e9d2984463e38e4c
> Reviewed-on: https://skia-review.googlesource.com/137903
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,jvanverth@google.com,bsalomon@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: skia:
Change-Id: Ia4b7c0bb2c7b5dba809d85c69f0b41b473140526
Reviewed-on: https://skia-review.googlesource.com/138181
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
13 files changed