Do no use custom gtkrc files in layout test mode....

webkit/tools/test_shell/test_shell_platform_delegate_gtk.cc

Index: webkit/tools/test_shell/test_shell_platform_delegate_gtk.cc
===================================================================
--- webkit/tools/test_shell/test_shell_platform_delegate_gtk.cc	(revision 8646)
+++ webkit/tools/test_shell/test_shell_platform_delegate_gtk.cc	(working copy)
@@ -14,6 +14,11 @@
 }
 
 void TestShellPlatformDelegate::SelectUnifiedTheme() {
+  // Stop custom gtkrc files from messing with the theme.
+  gchar* default_gtkrc_files[] = { NULL };
+  gtk_rc_set_default_files(default_gtkrc_files);
+  gtk_rc_reparse_all_for_settings(gtk_settings_get_default(), TRUE);
+
   // Pick a theme that uses Cairo for drawing, since we:
   // 1) currently don't support GTK themes that use the GDK drawing APIs, and
   // 2) need to use a unified theme for layout tests anyway.