Reland DeferredTextureImageData low-bit-depth/dithering support

Cause DeferredTextureImageData functionality to support low bit depth
(4444, 565) image formats (with dithering).

Updated to handle colorspace + 4444 colortype correctly.

Bug: 720105
Change-Id: Ib7e14d937849f4f6b08fda6992a240bb203d0089
Reviewed-on: https://skia-review.googlesource.com/19094
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
7 files changed