move the guts of SkMaskFilter.h into SkMaskFilterBase.h

Bug: skia:
Change-Id: I29ad0960156562867429542d3cfbf3d639529cab
Reviewed-on: https://skia-review.googlesource.com/98802
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
31 files changed