In makeColorSpace, hoist the null -> sRGB optimization

Clean up all the onMakeColorSpace implementations a bit.

Bug: skia:
Change-Id: I31f32fa711a3af38bd697886379b23cc703cf864
Reviewed-on: https://skia-review.googlesource.com/c/162030
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
4 files changed