Show an error update engine status for all unknown states.
Show an error update engine status for all unknown states.

The primary reason for this patch is so that I can add a new UPDATE_STATUS
enum value to libcros without breaking the Chrome OS build with the following
error:

"Right now we get the following error with LKGR of Chrome:
update_observer.cc: In member function 'virtual void
chromeos::UpdateObserver::Changed(chromeos::UpdateLibrary*)':
update_observer.cc:26: error: enumeration value
'UPDATE_STATUS_REPORTING_ERROR_EVENT' not handled in switch"

BUG=560
TEST=emerged chromeos-chrome with modified libcros, unit tests

Review URL: http://codereview.chromium.org/3053010

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@53409 0039d316-1c4b-4281-b951-d872f2087c98

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