packages/firebase_messaging/android/src/main/AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="io.flutter.plugins.firebasemessaging"
  android:versionCode="1"
  android:versionName="0.0.1">

  <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="21" />

  <application>
    <service android:name=".FlutterFirebaseInstanceIDService">
      <intent-filter>
        <action android:name="com.google.firebase.INSTANCE_ID_EVENT"/>
      </intent-filter>
    </service>
    <service android:name=".FlutterFirebaseMessagingService">
      <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT"/>
      </intent-filter>
    </service>
  </application>
</manifest>