add lisence header

packages/shared_preferences/android/src/main/java/io/flutter/plugins/sharedpreferences/MethodCallHandlerImpl.java

@@ -1,3 +1,7 @@
+// Copyright 2019 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.
+
 package io.flutter.plugins.sharedpreferences;
 
 import android.content.Context;

packages/shared_preferences/example/android/app/src/main/java/dev/flutter/plugins/sharedpreferencesexample/MainActivity.java

@@ -1,3 +1,7 @@
+// Copyright 2019 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.
+
 package dev.flutter.plugins.sharedpreferencesexample;
 
 import dev.flutter.plugins.sharedpreferences.SharedPreferencesPlugin;