Forward declare CSSAnimationUpdate in StyleResolverState

This significantly speeds up incremental compiles when working on
animations, dropping the steps required from ~700 to ~50. Note
that the various un-inlined functions were moved as destructing
OwnPtr and PassOwnPtr objects requires the compiler to have the
pointed-to object's destructor available.

BUG=

Review URL: https://codereview.chromium.org/132693005

git-svn-id: svn://svn.chromium.org/blink/trunk@165440 bbb929c8-8fbe-4397-9dbb-9b2b20218538