Revert "Revert "Add GrRenderTargetContext instantiate & asTextureProxy""

Revert "Revert "Add GrRenderTargetContext instantiate & asTextureProxy""

This reverts commit 7d7d7d19462b75f5470492dc4820a02c1eba4af2.

Reason for revert: Reverting this to see if it really was crashing on SVGs or if that was cross talk.

Original change's description:
> Revert "Add GrRenderTargetContext instantiate & asTextureProxy"
>
> This reverts commit 9113edfff89e657dabc0ba095c54f7720550196c.
>
> Reason for revert: Looks to be causing EXCEPTION_ACCESS_VIOLATION:
>
> https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Win-MSVC-NUC-GPU-IntelIris6100-x86_64-Debug/builds/121/steps/test_skia%20on%20Windows/logs/stdio
> https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Win-MSVC-GCE-CPU-AVX2-x86-Debug/builds/2384/steps/test_skia%20on%20Windows-2008ServerR2-SP1/logs/stdio
> https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Win-MSVC-ShuttleC-GPU-iHD530-x86_64-Debug/builds/785/steps/test_skia%20on%20Windows/logs/stdio
>
> Original change's description:
> > Add GrRenderTargetContext instantiate & asTextureProxy
> >
> > This CL also centralizes the instantiation code in GrSurfaceProxy and adds a test.
> >
> > GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4494
> >
> > Change-Id: I0081d9a216dc0af293179f23bcb88acf6a822324
> > Reviewed-on: https://skia-review.googlesource.com/4494
> > Reviewed-by: Brian Salomon <bsalomon@google.com>
> > Commit-Queue: Robert Phillips <robertphillips@google.com>
> >
>
> TBR=bsalomon@google.com,robertphillips@google.com,reviews@skia.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Change-Id: I225ce7867ebd445067e5ea55ebbfd587f7fe782a
> Reviewed-on: https://skia-review.googlesource.com/4528
> Commit-Queue: Leon Scroggins <scroggo@google.com>
> Reviewed-by: Leon Scroggins <scroggo@google.com>
>

TBR=bsalomon@google.com,robertphillips@google.com,scroggo@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: Ifc3b9ac343009a3808f5f47500eef50df438e3d9
Reviewed-on: https://skia-review.googlesource.com/4537
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>