fix labels in P3 gm

We first draw interpolating in P3, UPM+PM, then in sRGB, UPM+PM.
Looks like the last gradient got its labels as a copy and paste
from the second.

Add a todo to test the middle color somehow.  That's where we
either are or were going wrong, and it's an easy way to test
interpolation.

Change-Id: Ib7ff385c9244e33ee13fd206279119de25ce2eb6
Reviewed-on: https://skia-review.googlesource.com/c/196581
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed