Make additive calculations more generic in preparation for keyframe additive…

Authored by featherless on Mar 20 2017, 2:56 PM.

Description

Make additive calculations more generic in preparation for keyframe additive animation support.

Summary: This also allows us to remove the Zeroable constraint on the coreAnimationSpringToStream API.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, Material Motion, chuga

Reviewed By: O4 Material Apple platform reviewers, chuga

Subscribers: chuga

Tags: Material Motion

Differential Revision: http://codereview.cc/D2890