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