[CRD iOS] Refactor an interface for RemotingAuthorization

remoting/ios/facade/remoting_service.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_IOS_FACADE_REMOTING_SERVICE_H_
 #define REMOTING_IOS_FACADE_REMOTING_SERVICE_H_
 
 #import "remoting/client/chromoting_client_runtime.h"
 
-#include "base/memory/weak_ptr.h"
-#include "remoting/base/oauth_token_getter.h"
-
 @class HostInfo;
 @class UserInfo;
-@class RemotingAuthentication;
+
+@protocol RemotingAuthentication;
 
 // Eventing related keys:
 
 // Hosts did update event.
 extern NSString* const kHostsDidUpdate;
 // User did update event name.
 extern NSString* const kUserDidUpdate;
 // Map key for UserInfo object.
 extern NSString* const kUserInfo;
 
 // |RemotingService| is the centralized place to ask for information about
 // authentication or query the remote services. It also helps deal with the
 // runtime and threading used in the application. |RemotingService| is a
 // singleton and should only be accessed via the |SharedInstance| method.
 @interface RemotingService : NSObject
 
 // Access to the singleton shared instance from this method.
-+ (RemotingService*)SharedInstance;
++ (RemotingService*)instance;
 
 // Start a request to fetch the host list. This will produce an notification on
 // |kHostsDidUpdate| when a new host is ready.
 - (void)requestHostListFetch;
 
-@property(nonatomic, readonly) RemotingAuthentication* authentication;
-
 // Returns the current host list.
 @property(nonatomic, readonly) NSArray<HostInfo*>* hosts;
 
 // The Chromoting Client Runtime, this holds the threads and other shared
 // resources used by the Chromoting clients
 @property(nonatomic, readonly) remoting::ChromotingClientRuntime* runtime;
 
+// This must be set immediately after the authentication object is created. It
+// can only be set once.
+@property(nonatomic) id<RemotingAuthentication> authentication;
+
 @end
 
 #endif  // REMOTING_IOS_FACADE_REMOTING_SERVICE_H_