CRD iOS: Adding pin entry view controller.

remoting/client/ios/app/pin_entry_view_controller.h

+// 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 REMOTING_CLIENT_IOS_APP_PIN_ENTRY_VIEW_CONTROLLER_H_
+#define REMOTING_CLIENT_IOS_APP_PIN_ENTRY_VIEW_CONTROLLER_H_
+
+#import <UIKit/UIKit.h>
+
+typedef void (^PinEntryModalCallback)(NSString* hostPin, BOOL createPairing);
+
+// PinEntryViewController is expected to be created, displayed and then
+// destroyed after the pin entry is finished; not reused.
+@interface PinEntryViewController : UIViewController
+
+// Callback will be used to return the pin entry result.
+- (id)initWithCallback:(PinEntryModalCallback)callback;
+
+@end
+
+#endif  // REMOTING_CLIENT_IOS_APP_PIN_ENTRY_VIEW_CONTROLLER_H_