Blink: Implement WebP YUV decoding and conditionally go down the path.

This change defines the logic to do WebP YUV decoding only
for lossy, non-alpha images without color profiles and only when
the kDecodeLossyWebPImagesToYUV flag is on. For now, we continue to
veto YUV decoding until all data is received because supporting
"incremental" YUV decoding in Chromium is a separate task
crbug.com/943519. It also adds a few initialization calls to
ImageFrameGenerator to set up plane sizes.

The YUV decoding path will initially be implemented for in-process
GPU rasterization and later for OOPR (Out of Process Rasterization).

See bit.ly/webp-decoding-into-yuv for the design document and
crrev.com/c/1338461 for a prototype CL summarizing all changes.

Bug: 900589
Change-Id: I7f40517273a62288a9bf0060176f864bf30d5aca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1393003


Commit-Queue: Madeleine Barowsky <mbarowsky@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Leon Scroggins <scroggo@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660545}