[chromeos] New PowerManagerClient observer to collect power data.

The observer currently only collects power supply data. This CL
should be treated as the first in a series to address the
marked issue.

BUG=312956

Review URL: https://codereview.chromium.org/101963004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241445 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241445
Implement ServiceManager

BUG=None
R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/93793009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241446 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241446