[Android] Re-enable NativeFileSystem instrumentation test

Root cause:
Instrument test loads test page as "Data URI scheme". Such type of URI
dosen't have URL origin. An empty URL origin will cause crash.

Fix:
Give a default value, "file:///", to URL origin to avoid crash.

Related to XWALK-99
In android webview, there is loadDataWithBaseUrl to cover such case, and for crosswalk, https://crosswalk-project.org/apis/embeddingapidocs_v2/reference/org/xwalk/core/XWalkView.html#load(java.lang.String, java.lang.String) is similar, have you tried this way?