imagefilters should take const array

Bug: skia:
Change-Id: I6f069c843ab27b41c4d1e87f76130e2ba2daf048
Reviewed-on: https://skia-review.googlesource.com/20211
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed