Pass a TaskRunner through ViewsDelegate to put AX init on FILE thread

ui/accessibility/platform/atk_util_auralinux.h

 // Copyright 2015 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.
 
 #ifndef UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_
 #define UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_
 
 #include "base/memory/singleton.h"
 #include "ui/accessibility/ax_export.h"
 
+namespace base {
+class TaskRunner;
+}
+
 namespace ui {
 
 // This singleton class initializes ATK (accessibility toolkit) and
 // registers an implementation of the AtkUtil class, a global class that
 // every accessible application needs to register once.
 class AtkUtilAuraLinux {
  public:
   // Get the single instance of this class.
   static AtkUtilAuraLinux* GetInstance();
 
   AtkUtilAuraLinux();
   virtual ~AtkUtilAuraLinux();
 
+  void Initialize(scoped_refptr<base::TaskRunner> init_task_runner);
+
  private:
   friend struct DefaultSingletonTraits<AtkUtilAuraLinux>;
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_