Add GetCurrentNativeController to webstate.

ios/web/public/test/native_controller_test_util.h

+// Copyright 2016 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.
+
+#ifndef IOS_WEB_PUBLIC_TEST_NATIVE_CONTROLLER_TEST_UTIL_H_
+#define IOS_WEB_PUBLIC_TEST_NATIVE_CONTROLLER_TEST_UTIL_H_
+
+#import "ios/web/public/web_state/web_state.h"
+
+@protocol CRWNativeContent;
+
+namespace web {
+namespace test {
+
+// Returns the native controller of the given |web_state|.
+id<CRWNativeContent> GetCurrentNativeController(WebState* web_state);
+
+}  // namespace test
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_TEST_NATIVE_CONTROLLER_TEST_UTIL_H_