Reland "Don't flatten images in SkImageShader"

This is a reland of 318afe66e699970ebf789718b5a2297f783ed712

Original change's description:
> Don't flatten images in SkImageShader
> 
> Bug: skia:9570
> 
> Change-Id: Idd4485b5c5814501fe98fbf2115d89a80a41f5c7
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299139
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>

Bug: skia:9570
Change-Id: I4761e354dd4ec4f4a60097e06c3b9b9b73e538f6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299681
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
3 files changed