Add Active Directory login UI tests

chromeos/dbus/fake_auth_policy_client.h

Index: chromeos/dbus/fake_auth_policy_client.h
diff --git a/chromeos/dbus/fake_auth_policy_client.h b/chromeos/dbus/fake_auth_policy_client.h
index 498d63792d136660b9c49e24f034b04199b0a2f3..d9cd1f167216843442cad762e0ba8170fb9c3b04 100644
--- a/chromeos/dbus/fake_auth_policy_client.h
+++ b/chromeos/dbus/fake_auth_policy_client.h
@@ -39,8 +39,13 @@ class CHROMEOS_EXPORT FakeAuthPolicyClient : public AuthPolicyClient {
   // devices.
   void set_started(bool started) { started_ = started; }
 
+  void set_auth_error(authpolicy::ErrorType auth_error) {
+    auth_error_ = auth_error;
+  }
+
  private:
   bool started_ = false;
+  authpolicy::ErrorType auth_error_ = authpolicy::ERROR_NONE;
   DISALLOW_COPY_AND_ASSIGN(FakeAuthPolicyClient);
 };