GitLab

Pressing the "Go back" button on the managed user block interstitial page closes the tab if there is no previous URL to go back to.

BUG=307215

Review URL: https://codereview.chromium.org/248963004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266982 0039d316-1c4b-4281-b951-d872f2087c98