Addapt tests to Chrome

[piranna]

If you run the test on Chrome, where there's native support for Filesystem API, the tests fails (ironic). They should be fixed so it could be detected and the pass on Chrome as reference, too.

[ebidel]

True story. This is a bit annoying, but requires some hackery in the library. For example,
the native window.TEMPORARY/PERISTENT is readonly and throws an exception if you try to overwrite it.