Summary:
Before this diff, `TouchOverlayView` would be an inner non-static class,so it'd be difficult to track memory ownership for it.
It also made `InspectorFlipperPlugin` longer and harder to read.
Reviewed By: cekkaewnumchai
Differential Revision: D22285744
fbshipit-source-id: 6fdd8c33a07be6ab900ebb28a8c3ebf3761fb598