Fix XWALK-1615 Cordova API test fails due to no JavaScript API exposed

Update the ExposedJsApi according to annotation of
XWalkView.addJavascriptInterface().
See https://crosswalk-project.org/jira/browse/XWALK-1596 for details.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1615