Summary:
Today, ReactInstanceManager calls `ReactChoreographer.initialize()` in its constructor. Since `ReactChoreographer` also needs to run on the UI thread, this forces the entire `ReactInstanceManager` to run on the UI thread.
By moving `ReactChoreographer` to lazily set up its Choreographer, we can make `ReactInstanceManager` run on any thread
Reviewed By: mdvacca
Differential Revision: D10097432
fbshipit-source-id: eb8c80aafcba745ea15c86296d11c487329b1df0
Ram N
5e7c774d64