Added support for corner radii in Android

Summary:
This is a cut down version of a previous pull request with just the 4 corners catered for.
Closes https://github.com/facebook/react-native/pull/4252

Reviewed By: svcscm

Differential Revision: D2911959

Pulled By: androidtrunkagent

fb-gh-sync-id: 7ddcd684d90d4d92ccefed906c0126e92818dcde

Examples/UIExplorer/BorderExample.js

@@ -98,6 +98,20 @@ var styles = StyleSheet.create({
     marginRight: 10,
     backgroundColor: 'lightgrey',
   },
+  border9: {
+    borderWidth: 10,
+    borderTopLeftRadius: 10,
+    borderBottomRightRadius: 20,
+    borderColor: 'black',
+  },
+  border10: {
+    borderWidth: 10,
+    backgroundColor: 'white',
+    borderTopLeftRadius: 10,
+    borderBottomRightRadius: 20,
+    borderColor: 'black',
+    elevation: 10
+  }
 });
 
 exports.title = 'Border';
@@ -180,4 +194,19 @@ exports.examples = [
       );
     }
   },
+  {
+    title: 'Corner Radii',
+    description: 'borderTopLeftRadius & borderBottomRightRadius',
+    render() {
+      return <View style={[styles.box, styles.border9]} />;
+    }
+  },
+  {
+    title: 'Corner Radii / Elevation',
+    description: 'borderTopLeftRadius & borderBottomRightRadius & elevation',
+    platform: 'android',
+    render() {
+      return <View style={[styles.box, styles.border10]} />;
+    }
+  },
 ];