[fixed] missing import
[fixed] missing import

Summary: Broke build when we changed from IndefiniteObservable to MotionObservable

Reviewers: O3 Material JavaScript platform reviewers, #material_motion, O2 Material Motion, featherless

Reviewed By: #material_motion, O2 Material Motion, featherless

Subscribers: featherless

Tags: #material_motion

Differential Revision: http://codereview.cc/D2388

material-motion/material-motion-js,material-motion/material-motion-js,material-motion/material-motion-js