Add NTPViewController to Showcase.

ios/showcase/ntp/sc_ntp_coordinator.h

Index: ios/showcase/ntp/sc_ntp_coordinator.h
diff --git a/ios/showcase/ntp/sc_ntp_coordinator.h b/ios/showcase/ntp/sc_ntp_coordinator.h
new file mode 100644
index 0000000000000000000000000000000000000000..ccc3094d8c162e59655b8887387a40864af3121e
--- /dev/null
+++ b/ios/showcase/ntp/sc_ntp_coordinator.h
@@ -0,0 +1,19 @@
+// Copyright 2017 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_SHOWCASE_NTP_SC_NTP_COORDINATOR_H_
+#define IOS_SHOWCASE_NTP_SC_NTP_COORDINATOR_H_
+
+#import <UIKit/UIKit.h>
+
+#import "ios/showcase/common/coordinator.h"
+
+@interface SCNTPCoordinator : NSObject<Coordinator>
+
+// Redefined to be a UINavigationController.
+@property(nonatomic, weak) UINavigationController* baseViewController;
+
+@end
+
+#endif  // IOS_SHOWCASE_NTP_SC_NTP_COORDINATOR_H_