Deprecate SaveFlags use in the public SkCanvas API.

Deprecate SaveFlags use in the public SkCanvas API.

Because we still have internal users for now (to support the deprecated
mode), this CL introduces an external-only variant of deprecation.

Chromium is no longer using the deprecated methods, but Android may need
to suppress SK_ATTR_EXTERNALLY_DEPRECATED warnings.

R=reed@google.com, robertphillips@google.com, scroggo@google.com, bungeman@google.com, mtklein@google.com

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/246023008

git-svn-id: http://skia.googlecode.com/svn/trunk@14367 2bbb7eff-a529-9590-31e7-b0007b416f81