chromeos: Explicitly initialize and shut down UpgradeDetectorChromeos.

chromeos: Explicitly initialize and shut down UpgradeDetectorChromeos.

The motivation is to solve a dependency issue between UpgradeDetectorChromeos
and DBusThreadManager, that'll replace CrosLibrary (i.e. UpgradeDetectorChromeos
will be using DBusThreadManager internally).

BUG=16564
TEST=Upgrade detector works as before. (create a new image, start dev server, and run update_engine_client --update, and confirm that an arrow is shown on the wrench menu icon, once the update is downloaded in the background).

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=110409

[stevenjb, 2011-11-16 01:04:40]

lgtm

[satorux1, 2011-11-16 07:10:05]

+Nikita for a minor change in 'login'.

The expectation is slightly changed as the first call to
UpdateLibrary::AddObserver() was delayed to the point where the mock can record
the first call.

[satorux1, 2011-11-17 00:32:08]

LGTM.

Please include chrome/browser/chromeos/system/runtime_environment.h from files
where IsRunningOnChromeOS() is used.

[satorux1, 2011-11-17 00:38:31]

Oops, I replied to a wrong code review issue...

[satorux1, 2011-11-17 02:50:00]

Hmm, I was able to commit the patch by "git cl dcommit" without any warnings
despite the fact that I didn't get LGTM from
chrome/browser/chromeos/login/OWNERS. This may be a bug in the presubmit system?