Add new auto-login UI.

When the WebView notifies us of an auto-login request, check if the account is
valid.  If so, use it to log into the account manager.  If that fails or the
account is not valid, display the login UI.

Bug: 3367381
Change-Id: I5a164ef676921eec03a89860fa5be722d3d987d4
11 files changed