Passwords: Reset re-authentication timer when password manager is re-opened.

When the user is re-authenticated before revealing a plaintext password, the
authentication state is remembered for one minute. If the password manager is
closed and re-opened, the user should be forced to re-authenticate again if
they want to reveal a password.

BUG=327331

Review URL: https://codereview.chromium.org/119083004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242192 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242192