update SkColor4f::FromColor() to preserve transfer function

This kills off some sRGB tables,
and lots of call sites can now use SkColor4f::FromColor().

It doesn't seem important to keep this test.

Change-Id: Ia79ec8ace45e80bbc7a1e33f560f59289e61b2fb
Reviewed-on: https://skia-review.googlesource.com/141046
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
8 files changed