Bug 819080 - Part 2: implement the b2gperf test.

@davehunt This is a *feedback request* for the implementation of new test.

A few things I need to polish

1. rename fmradio.js to something else 
1. make it more generic to allow other apps
1. Have a better way to wait for the logcat entry

The original bugzilla is https://bugzilla.mozilla.org/show_bug.cgi?id=819080