Expose setAllowUniversalAccessFromFileURLs in Android WebView

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

Libraries/Components/WebView/WebView.android.js

@@ -152,6 +152,14 @@ class WebView extends React.Component {
      * start playing. The default value is `false`.
      */
     mediaPlaybackRequiresUserAction: PropTypes.bool,
+
+    /**
+     * Boolean that sets whether JavaScript running in the context of a file
+     * scheme URL should be allowed to access content from any origin.
+     * Including accessing content from other file scheme URLs
+     * @platform android
+     */
+    allowUniversalAccessFromFileURLs: PropTypes.bool,
   };
 
   static defaultProps = {
@@ -227,6 +235,7 @@ class WebView extends React.Component {
         onLoadingError={this.onLoadingError}
         testID={this.props.testID}
         mediaPlaybackRequiresUserAction={this.props.mediaPlaybackRequiresUserAction}
+        allowUniversalAccessFromFileURLs={this.props.allowUniversalAccessFromFileURLs}
       />;
 
     return (