[uber page] Uber page updates for the 'Users' section, pointer overlay fixes.

- Change the 'accounts' page to appear as a sub-page.
- Show the sync UI in the the 'Users' section for ChromeOS.
- Make the 'Users' section match the mocks on ChromeOS.
- Fix: only hide the profiles UI, not the whole users section.
- Fix: Move some handling for device detection from browser_options to pointer_overlay.

BUG=107484,109217
Review URL: https://chromiumcodereview.appspot.com/9249038

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@118378 0039d316-1c4b-4281-b951-d872f2087c98
10 files changed