1. In the FusedPrintersLoader we start observing the printers on
the device and if they change we send the result. If however,
the printers are already loaded in our session (because it
joined an ongoing printer discovery) and the pritners do not
change, the loader never sends its result. Now we are registring
the callback only after historical printers are loaded. We
also immediately check after starting discovery whether the
there are printers in the discovery session and if so deliver
them.
2. Improved logging in the FusedPrintersLoader.
bug:10940712
Change-Id: Ieb9b897d64780742125b29309462dea3eda170a6
953c4143e8