Add evenly spaced stops and unify gradient contexts

Change-Id: I17ac13b9d1ea6765e2c1a2b53aa6975eab408856
Reviewed-on: https://skia-review.googlesource.com/16713
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
8 files changed