Make SkPaintFilterCanvas paints no longer COW.

The two existing external users of SkPaintFilterCanvas always end up
making a copy of the paint when the canvas is in use. As a result, the
extra overhead of doing COW is being wasted. In general, it seems easier
for users to optimize by simply not using the filter canvas when it
won't be making any changes. Also, no users are using the 'Type'.

After users are updated to this new API, the old onFilter can be
removed.

Change-Id: Iee1ce3cd22bce8c00664de078375b105abd7c866
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/149806
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
5 files changed