Uber tray unresponsive with Multiprofile enabled

In ExistingUserController::PerformLogin(), There was a missing call to
ExistingUserController::PerformLoginFinishedActions(), which should
re-enables clicking on the status tray after it has been disabled in
ExistingUserController::PerformPreLoginActions().

BUG=427047
TEST=manual

Review URL: https://codereview.chromium.org/682103002

Cr-Commit-Position: refs/heads/master@{#301975}

chrome/browser/chromeos/login/ui/login_display_host_impl.cc

@@ -1118,6 +1118,10 @@ void LoginDisplayHostImpl::ResetLoginWindowAndView() {
     return;
   login_window_->Close();
   login_window_ = NULL;
+
+  if (!login_view_)
+    return;
+  login_view_->SetUIEnabled(true);
   login_view_ = NULL;
 }