Use Skia's YUV readback API

This CL makes SkiaOutputSurfaceImpl use Skia's YUV readback API instead
of doing an RGB readback and a conversion afterwards. This CL also adds
a feature to always use Skia's API for readback instead of
GLRendererCopier, which is useful for testing Skia's GL readback and
doing finch trials later on.

Bug: 898595
Change-Id: I493edc8f2a406f0b015b1dfa580d41c97a088f34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643501
Commit-Queue: Saman Sami <samans@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668455}
4 files changed