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

webkit/tools/test_shell/test_shell_platform_delegate_gtk.cc

 // Copyright (c) 2009 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.
 
 #include <stdlib.h>  // required by _set_abort_behavior
 #include <gtk/gtk.h>
 
 #include "base/command_line.h"
 #include "webkit/tools/test_shell/test_shell.h"
 #include "webkit/tools/test_shell/test_shell_platform_delegate.h"
 
 void TestShellPlatformDelegate::PreflightArgs(int *argc, char ***argv) {
   gtk_init(argc, argv);  
 }
 
 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.
   g_object_set(gtk_settings_get_default(),
                "gtk-theme-name", "Mist",
                NULL);
 }
 
 TestShellPlatformDelegate::TestShellPlatformDelegate(
     const CommandLine& command_line)
     : command_line_(command_line) {
 }
 
 bool TestShellPlatformDelegate::CheckLayoutTestSystemDependencies() {
   return true;
 }
 
 void TestShellPlatformDelegate::SuppressErrorReporting() {
 }
 
 void TestShellPlatformDelegate::InitializeGUI() {
 }
 
 void TestShellPlatformDelegate::SetWindowPositionForRecording(TestShell *) {
 }
 
 TestShellPlatformDelegate::~TestShellPlatformDelegate() {
 }