Summary:
This pull request fixes cases where the `error` argument of the `onUnhandled` method in `Libraries/Promise.js` is undefined. Previously this would result in a redbox with the helpful message: `Cannot read property message of undefined`. With this pull request, unhandled promise rejections result in the desired yellowbox saying that a promise rejection went unhandled.
I still do not know what would cause the error argument to be undefined, but this change makes the module behave as expected in an app I am building.
cc bestander
Relevant issue: #8452
Closes https://github.com/facebook/react-native/pull/9119
Differential Revision: D3655589
Pulled By: bestander
fbshipit-source-id: a975a0ab58701240ba06574c04521cd542700ff7
591217ea7d