Make the new Gaia password separated signin flow modal.

chrome/browser/ui/cocoa/browser_window_cocoa.h

Index: chrome/browser/ui/cocoa/browser_window_cocoa.h
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa.h b/chrome/browser/ui/cocoa/browser_window_cocoa.h
index 43f633c47fb4d9d1cc3ee9a9b6e2073ecb73fd54..cb3863dfec8943645ef3bb69689dad89401db9fc 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.h
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.h
@@ -158,6 +158,8 @@ class BrowserWindowCocoa
   void ShowAvatarBubbleFromAvatarButton(
       AvatarBubbleMode mode,
       const signin::ManageAccountsParams& manage_accounts_params) override;
+  void ShowModalSigninWindow(AvatarBubbleMode mode) override;
+  void CloseModalSigninWindow() override;
   int GetRenderViewHeightInsetWithDetachedBookmarkBar() override;
   void ExecuteExtensionCommand(const extensions::Extension* extension,
                                const extensions::Command& command) override;