battery-status: Implement the battery-status API for chromeos.

This patch changes BatteryStatusManager to be a pure interface, and moves
platform-specific sub-classes to provide the necessary implementations.

BUG=122593
TEST=manual, using http://jsbin.com/battery-status-diagnostics
R=brettw@chromium.org, jdduke@chromium.org, timvolodine@chromium.org

Review URL: https://codereview.chromium.org/356873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283015 0039d316-1c4b-4281-b951-d872f2087c98
12 files changed