Summary:
This pull request exposes the `setAllowUniversalAccessFromFileURLs` method of Android WebViewSettings as a property. The reason for this is when loading pages with a `file://` baseUrl it's sometimes desirable to allow loading other assets from a file base url. (For example loading an image into a canvas). More information on its use and purpose can be found [in the android docs here](https://developer.android.com/reference/android/webkit/WebSettings.html#setAllowUniversalAccessFromFileURLs%28boolean%29)
Usage example:
``` jsx
return (
<WebView
source={{ html: myhtml, baseUrl: 'file://' }}
allowUniversalAccessFromFileURLs={true}
javaScriptEnabled={true} />
)
```
Closes https://github.com/facebook/react-native/pull/8905
Differential Revision: D4147245
Pulled By: hramos
fbshipit-source-id: 7eaa884b8c0268de52b284954a34acec0fbd4061
b6a38e80e0