[CB-2213] Added a new test for readAsDataURL.
[CB-2213] Added a new test for readAsDataURL.

This test uses a FileEntry created using a native URI.

ollie314/cordova-mobile-spec,corimf/cordova-mobile-spec,polyvi/xface-mobile-spec,polyvi/xface-mobile-spec,corimf/cordova-mobile-spec,ollie314/cordova-mobile-spec,lorinbeer/cordova-mobile-spec,corimf/cordova-mobile-spec,corimf/cordova-mobile-spec,ollie314/cordova-mobile-spec,corimf/cordova-mobile-spec,ollie314/cordova-mobile-spec,ollie314/cordova-mobile-spec,polyvi/xface-mobile-spec,apache/cordova-mobile-spec,apache/cordova-mobile-spec,apache/cordova-mobile-spec,apache/cordova-mobile-spec,apache/cordova-mobile-spec