[changed] Scheduler to reuse performers across transactions
[changed] Scheduler to reuse performers across transactions

Summary:
Each call to `commit` was previously operating independently, which caused new performers to be made for each transaction, even when an existing performer could do the job.

This commit moves that pipeline out of `commit` and up to the instance level, which allows performers to be reused across commits.

Fixed https://github.com/material-motion/material-motion-experiments-js/issues/41

Reviewers: featherless, O3 JavaScript reviewers, shyndman

Reviewed By: O3 JavaScript reviewers, shyndman

Differential Revision: http://codereview.cc/D1334

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