GitLab

This makes Chrome listen for messages from the power manager
asking it to dim or undim the screen.  We'll use this on
desktop devices with external displays to dim the screen
just before blanking it when the user is idle.

BUG=125176
TEST=added, also did manual testing with powerd changes


Review URL: http://codereview.chromium.org/10263011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@134638 0039d316-1c4b-4281-b951-d872f2087c98