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

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

Index: chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h
diff --git a/chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h b/chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h
index d5328a3463112d18eb4342ac1fc9fac0d949c18f..d6c3ee71028f176ab07999fc0f642883230d1dc0 100644
--- a/chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h
+++ b/chrome/browser/ui/cocoa/passwords/account_chooser_view_controller.h
@@ -20,12 +20,15 @@ class PasswordPromptBridgeInterface;
 // 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