GTK: Seal up GSEALs, focusing on GtkSelectionData.

ui/gfx/screen_gtk.cc

Index: ui/gfx/screen_gtk.cc
diff --git a/ui/gfx/screen_gtk.cc b/ui/gfx/screen_gtk.cc
index 579ad1a2852413d5f81e38da35bb6a1dd95ef4b0..1607cc8ea8f1ce2db4ff3e18883ccb5b9872ff70 100644
--- a/ui/gfx/screen_gtk.cc
+++ b/ui/gfx/screen_gtk.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -80,7 +80,9 @@ gfx::Rect Screen::GetMonitorAreaNearestWindow(gfx::NativeView view) {
     DCHECK(GTK_IS_WINDOW(top_level));
     GtkWindow* window = GTK_WINDOW(top_level);
     screen = gtk_window_get_screen(window);
-    monitor_num = gdk_screen_get_monitor_at_window(screen, top_level->window);
+    monitor_num = gdk_screen_get_monitor_at_window(
+        screen,
+        gtk_widget_get_window(top_level));
   }
   GdkRectangle bounds;
   gdk_screen_get_monitor_geometry(screen, monitor_num, &bounds);