Adds some logging to GWTTestCase at level FINE.

Patch also includes some fixes to test cases that revealed itself
when the Logger is added.
The cluprit of breakage was; DevMode was failed to execute some JSNI calls
(e.g. window.console.log) when document body is cleared.

Change-Id: Idb501edcb83c1e150804f1619024072cec1d6de3