Use a new domstorage-flush-force message for testing calling
FlushAndDeleteTemporaryTables with a 'true' argument. We want to add more
work to profile-before-change and that would interfere with the testing
in dom/tests/mochitest/localstorage/test_bug624047.html.
Also move the NS_DOMSTORAGE_FLUSH_TIMER_OBSERVER define to the .cpp file
since that is the only place it is used and rename it to end in _TOPIC.