update SkShader appendStages() fallback plan

This version makes these shaders draw differently, shading in sRGB then
transforming to dst, rather than transforming all inputs to dst then
shading.

There aren't many shaders that fall into this path (perlin noise and
lighting shader only?), and I think the legacy, sRGB, and even esRGB
paths should draw the same, so it may be we can kind of just slip this
through?

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: I0860f9f43c5ed8962fb0fe9405c15e664232dde9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/202724
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed