Make gradient effect creation fail if texture LUT creation fails

Bug: skia:6198
Change-Id: Ib8fb273564ca54ee9e6e045ac67e191af705a37a
Reviewed-on: https://skia-review.googlesource.com/19260
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
7 files changed