Making app_tab_helper_ multi profile aware

This pitch is ridding the first of the single profile dependencies from the launcher.

BUG=299165
TEST=unittest

Review URL: https://codereview.chromium.org/24998012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226115 0039d316-1c4b-4281-b951-d872f2087c98
ash: Rename guest wallpaper flags.

Rename --ash-default-guest-wallpaper-{large,small} to
--ash-guest-wallpaper-{large,small}
(session_manager_setup.sh is currently passing both the old
and new flags). "Default" doesn't make sense here since
guest wallpapers aren't user-configurable.

BUG=298389

Review URL: https://codereview.chromium.org/25329002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226116 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226116