Redirect to NTP when "sign in with different email" confirmation dialog is closed.

Redirect to NTP when "sign in with different email" confirmation dialog is closed.

With this CL, the user is never left on a blank page when the "sign in
with different email" confirmation dialog is closed. The tab is
redirected to the NTP or Apps page instead.

TEST=
Pre-Condition: User is logged in Chrome.
1.Go To chrome://settings and click on "Disconnect Your Google Account" to get disconnected from Chrome.
2.Click on "Sign in to chrome", and click on "Sign Out and Sign in as Different user".
3.Sign in with a different user in Chrome.
3.A confirmation overlay window about "someone already logged in" appears. Close this window and observe.
Expected result: The NTP is displayed. The user is not left on a blank page.
BUG=271423

Review URL: https://chromiumcodereview.appspot.com/23746002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@220391 0039d316-1c4b-4281-b951-d872f2087c98