4/n: Add basic enrollment for Face

Bug: 110589286

Test: fingerprint enrolling still works
Test: enrollment flow with and without a pin set up still works properly
Test: enrollment continues when configuration changes, stops otherwise

Change-Id: I39f76c7f1a16e9533cef573f87cf4b81cb20cb18

res/layout/face_enroll_enrolling_footer.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2018 The Android Open Source Project
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License
+  -->
+
+<!-- TODO: Use aapt:attr when it is fixed (b/36809755) -->
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    style="@style/SuwGlifButtonBar"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content">
+
+    <Button
+        style="@style/SuwGlifButton.Secondary"
+        android:id="@+id/skip_button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="@string/security_settings_face_enroll_enrolling_skip" />
+
+</LinearLayout>