Make the new Gaia password separated signin flow modal.

chrome/browser/ui/cocoa/browser_window_cocoa.mm

Index: chrome/browser/ui/cocoa/browser_window_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa.mm b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
index 0c703069800de2d6037697ce85605940f6d9b3f2..a19146fbd75b2bee92fd84ecc98beec78347b375 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
@@ -833,6 +833,13 @@ void BrowserWindowCocoa::ShowAvatarBubbleFromAvatarButton(
                          withServiceType:manage_accounts_params.service_type];
 }
 
+void BrowserWindowCocoa::ShowModalSigninWindow(AvatarBubbleMode mode) {
+  NOTREACHED();
+}
+void BrowserWindowCocoa::CloseModalSigninWindow() {
+  NOTREACHED();
+}
+
 int
 BrowserWindowCocoa::GetRenderViewHeightInsetWithDetachedBookmarkBar() {
   if (browser_->bookmark_bar_state() != BookmarkBar::DETACHED)