chrome/android/java/res/layout/signin_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2018 The Chromium Authors. All rights reserved.
     Use of this source code is governed by a BSD-style license that can be
     found in the LICENSE file. -->
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>