Add a modal confirmation dialog to the enterprise profile sign-in flow.

When signing in with an enterprise user account, the user is prompted to
create a new Chrome profile, continue signing in with the current
profile, or cancel the signin process.

BUG=171236
TBR=jhawkins

Review URL: https://codereview.chromium.org/12221111

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@182702 0039d316-1c4b-4281-b951-d872f2087c98
13 files changed