change gm to use srgb (not linear) so srgb and legacy draw the same

Before this, the legacy run of the gm didn't draw the 2nd half, making
triaging confusing. Plus, we may not really care about testing the linear
part so much any more.

Bug: skia:
Change-Id: Iecea68eae9aa6e1c93d75d9d510d5c70aae648e3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/198163
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed