Wide color gamut support and working example.

Color space arguments accepted at surface creation, paint, gradient, and other call sites.
Works correctly only when chrome happens to be rendering itself in the same color space
the canvaskit user has chosen, there's not yet end to end color management of
canvases supported in browsers.

readPixels not yet working due to possible chrome bug.

Change-Id: I3dea5b16c60a3871cd2a54f86716f4a438a90135
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/289733
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
10 files changed