ash: Resize PowerButtonController background layer.

PowerButtonController wasn't getting registered as an
observer on the aura::RootWindow, so its background layer
wasn't resized to match the root window's size.  I don't
think that this caused any problems in practice, as the
layer gets recreated every time it's shown.

BUG=none
TEST=added


Review URL: http://codereview.chromium.org/10263015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@134722 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed