chromeos: Avoid notification for original Spring charger.

Fix a bug that resulted in "Battery full" notifications
being shown when using an original Spring charger.

BUG=338376

Review URL: https://codereview.chromium.org/148113004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247397 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247397