[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
fileapi::GetIsolatedFileSystemName() and fileapi::GetIsolatedFileSystemRootURIString() are under content. They cannot be modified. But I can test the scheme of the URL/URI. If the scheme is "data", assign "file:///" to origin. If not, take the normal way.