Implement lazy initialization for VrShellDelegate

device/vr/android/gvr/gvr_delegate.h

 // Copyright 2016 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 DEVICE_VR_ANDROID_GVR_DELEGATE_H
 #define DEVICE_VR_ANDROID_GVR_DELEGATE_H
 
 #include "device/vr/android/gvr/gvr_device_provider.h"
 #include "device/vr/vr_export.h"
 #include "device/vr/vr_service.mojom.h"
@@ skipping 19 matching lines @@
   virtual void CreateVRDisplayInfo(
       const base::Callback<void(mojom::VRDisplayInfoPtr)>& callback,
       uint32_t device_id) = 0;
 
  protected:
   virtual ~GvrDelegate() {}
 };
 
 class DEVICE_VR_EXPORT GvrDelegateProvider {
  public:
-  static void SetInstance(GvrDelegateProvider* delegate_provider);
+  static void SetInstance(
+      const base::Callback<GvrDelegateProvider*()>& provider_callback);
   static GvrDelegateProvider* GetInstance();
 
   virtual void SetDeviceProvider(GvrDeviceProvider* device_provider) = 0;
   virtual void ClearDeviceProvider() = 0;
   virtual void RequestWebVRPresent(
       const base::Callback<void(bool)>& callback) = 0;
   virtual void ExitWebVRPresent() = 0;
   virtual GvrDelegate* GetDelegate() = 0;
   virtual void SetListeningForActivate(bool listening) = 0;
 
  protected:
   virtual ~GvrDelegateProvider() {}
 
  private:
-  static GvrDelegateProvider* delegate_provider_;
+  static base::Callback<GvrDelegateProvider*()> delegate_provider_;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_VR_ANDROID_GVR_DELEGATE_H