Implement clone() for Gradient GrFragmentProcessors

Also removes the hard stop gradient conditional compilation macro.

Change-Id: Idd56b5f3061db063d650a0090406ec192acc0b53
Reviewed-on: https://skia-review.googlesource.com/27661
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
6 files changed