Temporarily restore old behavior of read/writeSurfacePixels

In the interest of only changing one thing at a time, this should fix the putImageData perf regression in Chrome. It will be followed up by a CL to change prepareSurfaceForExternalIO to always flush (which could have a different perf impact).

On Chrome's putImageData benchmark we get:

w/o this CL: avg 293.1247823176651 runs/s
w/  this CL: avg 374.8427288397461 runs/s

Bug: 942538
Change-Id: I9b9bc752532890f4313a45e5a6aa34b915d5e43d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205003
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
12 files changed