Summary:
Previously the bridge sometimes never fired RCTJavaScriptDidLoadNotification or RCTJavaScriptDidFailToLoadNotification if there was an error (for example, if the source code loaded but we couldn't inject the JSON config). This diff moves the error handling into a method called `stopLoadingWithError` that the bridge can call whenever there is an error.
Also if the script failed to load, the BatchedBridge still called `executeSourceCode`. With this diff the `_loading` flag is set to NO when the script fails to load, and `executeSourceCode` returns immediately when `_loading` is false. This way the bridge does not try to execute JS when there is a loading error.
Closes https://github.com/facebook/react-native/pull/2520
Github Author: James Ide <ide@jameside.com>