Summary: Introduces an API to register a weakly-held listener for the reload (Cmd+R) command. This allows external infrastructure to hook into the reload command before the `RCTBridge` object is even created.
Reviewed By: javache
Differential Revision: D4286980
fbshipit-source-id: 51012fb8cbeb433dc880d9d98d847b07fdbb4c4f
Adam Ernst