Revert "Rm readPixels from GrSurface & move read/writeSurfacePixels to GrContextPriv (take 2)"

This reverts commit aaee31f18c0845417103d84285e365575def3c40.

Reason for revert: possible valgrind leak

Original change's description:
> Rm readPixels from GrSurface & move read/writeSurfacePixels to GrContextPriv (take 2)
> 
> This is in service of: https://skia-review.googlesource.com/c/11125/ (Add parallel proxyID to StencilOps & RenderTargetOpList) where I want a better choke point for texture creation to improve discard handling.
> 
> This is a reland of: https://skia-review.googlesource.com/c/11200/ (Rm readPixels from GrSurface & move read/writeSurfacePixels to GrContextPriv)
> 
> Change-Id: Icd0a90d2beb483dc24ed87c3bace9c817019e148
> Reviewed-on: https://skia-review.googlesource.com/11326
> 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: Ia0b92bf6402cb5f9607310d356f43bff2e3e75eb
Reviewed-on: https://skia-review.googlesource.com/11361
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
30 files changed