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

ui/accessibility/platform/ax_platform_node_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_PLATFORM_NODE_AURALINUX_H_
 #define UI_ACCESSIBILITY_AX_PLATFORM_NODE_AURALINUX_H_
 
 #include <atk/atk.h>
 
+#include "base/memory/ref_counted.h"
 #include "ui/accessibility/ax_export.h"
 #include "ui/accessibility/platform/ax_platform_node_base.h"
 
+namespace base {
+class TaskRunner;
+}
+
 namespace ui {
 
 // Implements accessibility on Aura Linux using ATK.
 class AXPlatformNodeAuraLinux : public AXPlatformNodeBase {
  public:
   AXPlatformNodeAuraLinux();
 
   // Set or get the root-level Application object that's the parent of all
   // top-level windows.
   AX_EXPORT static void SetApplication(AXPlatformNode* application);
   static AXPlatformNode* application() { return application_; }
 
+  // Do static initialization using the given task runner for file operations.
+  AX_EXPORT static void StaticInitialize(
+      scoped_refptr<base::TaskRunner> init_task_runner);
+
   AtkRole GetAtkRole();
   void GetAtkState(AtkStateSet* state_set);
   void GetAtkRelations(AtkRelationSet* atk_relation_set);
 
   // AXPlatformNode overrides.
   void Destroy() override;
   gfx::NativeViewAccessible GetNativeViewAccessible() override;
   void NotifyAccessibilityEvent(ui::AXEvent event_type) override;
 
   // AXPlatformNodeBase overrides.
   void Init(AXPlatformNodeDelegate* delegate) override;
   int GetIndexInParent() override;
 
  private:
   ~AXPlatformNodeAuraLinux() override;
 
   // We own a reference to this ref-counted object.
   AtkObject* atk_object_;
 
   // The root-level Application object that's the parent of all
   // top-level windows.
   static AXPlatformNode* application_;
 
   DISALLOW_COPY_AND_ASSIGN(AXPlatformNodeAuraLinux);
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_PLATFORM_NODE_AURALINUX_H_