Update Android card unmasking prompt for the expiration date case.

ui/android/java/res/layout/autofill_card_unmask_prompt.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2014 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.
 -->
 
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:orientation="vertical">
 
     <TextView
         android:id="@+id/instructions"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:textSize="20sp"
-        android:paddingStart="5dp"
-        android:paddingEnd="5dp"
-        android:paddingBottom="5dp"
-        android:paddingTop="5dp"
+        android:textSize="16sp"
+        android:layout_marginStart="24dp"
+        android:layout_marginEnd="10dp"
+        android:layout_marginBottom="8dp"
+        android:layout_marginTop="10dp"
         android:gravity="start" />
 
     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="horizontal">
 
+        <!-- TODO(estade): add accessibility content descriptions. -->
+        <Spinner
+            android:id="@+id/expiration_month"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="16dp"
+            android:visibility="gone" />
+
+        <Spinner
+            android:id="@+id/expiration_year"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="16dp"
+            android:visibility="gone" />
+
         <EditText
             android:id="@+id/card_unmask_input"
             android:inputType="number"
             android:layout_height="wrap_content"
             android:layout_width="wrap_content"
             android:layout_marginStart="16dp"
             android:layout_marginEnd="16dp"
             android:ems="4"
             android:hint="@string/card_unmask_input_hint" />
 
@@ skipping 16 matching lines @@
         <TextView
             android:id="@+id/verification_message"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center_vertical"
             android:gravity="start"
             android:visibility="gone" />
      </LinearLayout>
 
 </LinearLayout>