[cros,de-hack] Get rid of singleton for the WebUILoginScreen.

chrome/browser/ui/webui/chromeos/login/base_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
index 9bc14cb867189d428288f00197b617cef09a784a..83cfcab6fe73687eb17e89ea06a7b2de3283d49d 100644
--- a/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "content/browser/webui/web_ui.h"
+#include "ui/gfx/native_widget_types.h"
 
 namespace base {
 class DictionaryValue;
@@ -39,6 +40,9 @@ class BaseScreenHandler : public WebUIMessageHandler {
   // Whether page is ready.
   bool page_is_ready() const { return page_is_ready_; }
 
+  // Returns the window which shows us.
+  gfx::NativeWindow GetNativeWindow();
+
  private:
   // Keeps whether page is ready.
   bool page_is_ready_;