Summary:
Fixes#4602
Fixes a bug where the app crashes when you try to inspect a stateless
component.
Fixed by replacing all occurrences of the getPublicInstance method in
Libraries/Inspector/Inspector.js with the _instance property instead.
Defaults to an empty object if _instance is falsy.
Closes https://github.com/facebook/react-native/pull/4642
Reviewed By: svcscm
Differential Revision: D2734491
Pulled By: androidtrunkagent
fb-gh-sync-id: 4ea753b7e0ef3fd05af2d80abadc365c5c787f98