Add color space xform to GrMagnifierEffect

Tag helper image as sRGB in magnifier image filter GM, so we can see
this working.

BUG=skia:

Change-Id: I8057dc332d09e1d508ad8462aaf0749b307f480f
Reviewed-on: https://skia-review.googlesource.com/6347
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed