Add "Sign In" button to the account chooser on Mac.

chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h

 // Copyright 2015 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 CHROME_BROWSER_UI_COCOA_PASSWORDS_ACCOUNT_CHOOSER_VIEW_CONTROLLER_H_
 #define CHROME_BROWSER_UI_COCOA_PASSWORDS_ACCOUNT_CHOOSER_VIEW_CONTROLLER_H_
 
 #import <Cocoa/Cocoa.h>
 
 #import "chrome/browser/ui/cocoa/passwords/password_prompt_bridge_interface.h"
 
 @class AccountAvatarFetcherManager;
 class PasswordPromptBridgeInterface;
 
 // Manages a view that shows a list of credentials that can be used for
 // authentication to a site.
 @interface AccountChooserViewController
     : NSViewController<PasswordPromptViewInterface, NSTextViewDelegate>
 @property(nonatomic) PasswordPromptBridgeInterface* bridge;
 // Initializes a new account chooser and populates it with the credentials
 // stored in |bridge->controller()|.
 - (instancetype)initWithBridge:(PasswordPromptBridgeInterface*)bridge;
+
+- (NSButton*)defaultButton;
 @end
 
 @interface AccountChooserViewController(Testing)
 - (instancetype)initWithBridge:(PasswordPromptBridgeInterface*)bridge
                  avatarManager:(AccountAvatarFetcherManager*)avatarManager;
 @property(nonatomic, readonly) NSButton* cancelButton;
+@property(nonatomic, readonly) NSButton* signInButton;
 @property(nonatomic, readonly) NSArray* credentialButtons;
 @property(nonatomic, readonly) NSTextView* titleView;
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_PASSWORDS_ACCOUNT_CHOOSER_VIEW_CONTROLLER_H_