Scrollbar color on supervised user creation screen is changed to be clear for user.

BUG=316568
NOTRY=true

Review URL: https://codereview.chromium.org/141543003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247668 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247668