Move RandomColor and RandomCoverage into GrTest.

These were declared as inline functions outside of the GrTest namespace
for some reason, but they are only used in test code and there doesn't
seem to be any reason for putting them in the header. (It doesn't seem
like they would benefit from being inlined.)

Change-Id: I4ba831168a0220d2eb550e08600159ba68220848
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/440519
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
9 files changed