Proof of concept of ignoring x-frame-options for sign-in webui.

chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc

Index: chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
===================================================================
--- chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc	(revision 248093)
+++ chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc	(working copy)
@@ -48,6 +48,7 @@
 #include "chrome/browser/ui/webui/signin/inline_login_ui.h"
 #include "chrome/browser/ui/webui/signin/profile_signin_confirmation_ui.h"
 #include "chrome/browser/ui/webui/signin/user_manager_ui.h"
+#include "chrome/browser/ui/webui/signin/signin_ui.h"
 #include "chrome/browser/ui/webui/signin_internals_ui.h"
 #include "chrome/browser/ui/webui/sync_internals_ui.h"
 #include "chrome/browser/ui/webui/translate_internals/translate_internals_ui.h"
@@ -320,6 +321,8 @@
       profile && profile->GetExtensionService()) {
     return &NewWebUI<AppLauncherPageUI>;
   }
+  if (url.host() == chrome::kChromeSigninHost)
+    return &NewWebUI<SigninUI>;
   // Bookmarks are part of NTP on Android.
   if (url.host() == chrome::kChromeUIBookmarksHost)
     return &NewWebUI<BookmarksUI>;