Short-circuit gradient color space conversion

... when src == dst

Change-Id: Idd62fb673105a62ee4d381a4dbc1d5117ce6abb9
Reviewed-on: https://skia-review.googlesource.com/63702
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed