Revert "Delete getRenderTargetHandle call on SkSurface."

This reverts commit c828109ebd1519134b1c3fa168519ac07a31fe05.

Reason for revert: Need to fix flutter

Original change's description:
> Delete getRenderTargetHandle call on SkSurface.
> 
> All clients and internal code should be switched (once changes land soon)
> to the new getBackendRenderTarget call instead.
> 
> Bug: skia:
> Change-Id: I6f490b6d26a72f37f97216be04e541483206510d
> Reviewed-on: https://skia-review.googlesource.com/121103
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

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

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

Bug: skia:
Change-Id: I571298f839757fcdedcd8117519e740ac7ef1344
Reviewed-on: https://skia-review.googlesource.com/121480
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
13 files changed