Gradient cleanup pass

1) replace manual storage management with SkAutoSTMalloc

2) simplify explicit positions processing (remove redundant branch)

Change-Id: I7841e2018ac421768ed1d61c4e3ef6a1d28f6244
Reviewed-on: https://skia-review.googlesource.com/66146
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed