Adding ChromeIdentity in ShowSigninCommand.

ios/chrome/browser/ui/commands/show_signin_command.mm

 // Copyright 2014 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.
 
 #import "ios/chrome/browser/ui/commands/show_signin_command.h"
 
 #include "base/logging.h"
 #include "ios/chrome/browser/ui/commands/ios_command_ids.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation ShowSigninCommand
 
 @synthesize operation = _operation;
+@synthesize identity = _identity;
 @synthesize accessPoint = _accessPoint;
 @synthesize promoAction = _promoAction;
 @synthesize callback = _callback;
 
 - (instancetype)initWithTag:(NSInteger)tag {
   NOTREACHED();
   return nil;
 }
 
 - (instancetype)initWithOperation:(AuthenticationOperation)operation
+                         identity:(ChromeIdentity*)identity
                       accessPoint:(signin_metrics::AccessPoint)accessPoint
                       promoAction:(signin_metrics::PromoAction)promoAction
                          callback:
                              (ShowSigninCommandCompletionCallback)callback {
   if ((self = [super initWithTag:IDC_SHOW_SIGNIN_IOS])) {
     _operation = operation;

[sdefresne, 2017/05/17 08:49:01]

Can you add a DCHECK to ensure the invariant that is described in the comment?
Something like this:

  DCHECK(
    (identity == nil && operation !=
AUTHENTICATION_OPERATION_SIGNIN_PROMO_CONTINUE_AS) ||
    (identity != nil && operation ==
AUTHENTICATION_OPERATION_SIGNIN_PROMO_CONTINUE_AS));

[jlebel, 2017/05/17 12:17:37]

Done.

+    _identity = identity;
     _accessPoint = accessPoint;
     _promoAction = promoAction;
     _callback = [callback copy];
   }
   return self;
 }
 
 - (instancetype)initWithOperation:(AuthenticationOperation)operation
                       accessPoint:(signin_metrics::AccessPoint)accessPoint
                       promoAction:(signin_metrics::PromoAction)promoAction {
   return [self initWithOperation:operation
+                        identity:nil
                      accessPoint:accessPoint
                      promoAction:promoAction
                         callback:nil];
 }
 
 @end