GitLab

This change introduces GetRasterSkImage() for use when an image's pixels
are needed in CPU memory for raster. The goal is to remove GetSkImage()
from PaintImage since, when texture backed, this API will incur the cost
of a GPU to CPU readback. GetRasterSkImage() makes it clear that this
readback may happen. Follow up changes will work on converting the
remaining callers of GetSkImage() to other APIs.

For details about this overall PaintImage effort, see crbug.com/1023259

This is being done as part of the OOPR-Canvas2D project. For more info
about that project see the tracking bug here: crbug.com/1018894

Bug: 1031050
Change-Id: Iae075b4c5d936ac7c6f3db578e6ef5c47b99ffd6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2226922Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: Jonah Chin <jochin@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#776226}