packages/SystemUI/res/layout/keyguard_bottom_area.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2014 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
  -->

<com.android.systemui.statusbar.phone.KeyguardBottomAreaView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:systemui="http://schemas.android.com/apk/res/com.android.systemui"
    android:id="@+id/keyguard_bottom_area"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:outlineProvider="none"
    android:elevation="5dp" > <!-- Put it above the status bar header -->

    <include layout="@layout/keyguard_indication_area_overlay" />

    <FrameLayout
        android:id="@+id/preview_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </FrameLayout>

    <com.android.systemui.statusbar.KeyguardAffordanceView
        android:id="@+id/camera_button"
        android:layout_height="@dimen/keyguard_affordance_height"
        android:layout_width="@dimen/keyguard_affordance_width"
        android:layout_gravity="bottom|end"
        android:src="@drawable/ic_camera_alt_24dp"
        android:scaleType="center"
        android:contentDescription="@string/accessibility_camera_button"
        android:tint="?attr/wallpaperTextColor" />

    <com.android.systemui.statusbar.KeyguardAffordanceView
        android:id="@+id/left_button"
        android:layout_height="@dimen/keyguard_affordance_height"
        android:layout_width="@dimen/keyguard_affordance_width"
        android:layout_gravity="bottom|start"
        android:src="@*android:drawable/ic_phone"
        android:scaleType="center"
        android:contentDescription="@string/accessibility_phone_button"
        android:tint="?attr/wallpaperTextColor" />

    <FrameLayout
        android:id="@+id/overlay_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <include layout="@layout/keyguard_bottom_area_overlay" />

    </FrameLayout>

</com.android.systemui.statusbar.phone.KeyguardBottomAreaView>