Align header in overlays in chrome://devices

Align overlay content with the overlay header in chrome://devices.

BUG=294341

Review URL: https://codereview.chromium.org/71483006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235567 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235567