refactor eden watcher
refactor eden watcher

Reviewed By: fanzeyi

Differential Revision: D30268727

fbshipit-source-id: 9c14176411e846a97d1825e7f025e9beda9b57b2

nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman