Factory methods for heap-allocated SkMaskFilter objects.

This is part of an effort to ensure that all SkPaint effects can only be
allocated on the heap.

This patch makes the constructors of SkMaskFilter and its subclasses non-public
and instead provides factory methods for  creating these objects on the heap. We
temporarily keep constructor of publicly visible classes public behind a flag.

BUG=skia:2187
R=scroggo@google.com, mtklein@google.com, reed@google.com

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/173633003

git-svn-id: http://skia.googlecode.com/svn/trunk@13527 2bbb7eff-a529-9590-31e7-b0007b416f81
10 files changed