Correct iOS build for latest Xcode beta.

ios/chrome/browser/xcallback_parameters.h

 // Copyright 2012 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_CHROME_BROWSER_XCALLBACK_PARAMETERS_H_
 #define IOS_CHROME_BROWSER_XCALLBACK_PARAMETERS_H_
 
 #import <Foundation/Foundation.h>
 
 #include "url/gurl.h"
 
 // This class contains the defining parameters for an XCallback request from
 // another app.
 @interface XCallbackParameters : NSObject<NSCoding, NSCopying>
 
 // The id of the calling app.
 @property(nonatomic, readonly, copy) NSString* sourceAppId;
 
 // The user visible name of the calling app. Can be nil.
 @property(nonatomic, readonly, copy) NSString* sourceAppName;
 
 // x-callback-url::x-success URL. If the app is opened using a x-callback-url
 // compliant URL, the value of this parameter is used as callback URL when the
 // user taps the back button.
 @property(nonatomic, readonly) const GURL& successURL;
 
 // Flag to force the creation of a new tab. Default YES.
 @property(nonatomic, readonly) BOOL createNewTab;
 
+- (instancetype)init NS_UNAVAILABLE;
+
 - (instancetype)initWithSourceAppId:(NSString*)sourceAppId
                       sourceAppName:(NSString*)sourceAppName
                          successURL:(const GURL&)successURL
                        createNewTab:(BOOL)createNewTab
     NS_DESIGNATED_INITIALIZER;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_XCALLBACK_PARAMETERS_H_