DOMWindow::navigator should return navigator w/o frame when detached.

Source/modules/vr/NavigatorVRDevice.cpp

 // 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.
 
 #include "config.h"
 #include "modules/vr/NavigatorVRDevice.h"
 
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Navigator.h"
 #include "core/page/Page.h"
 #include "modules/vr/HMDVRDevice.h"
 #include "modules/vr/PositionSensorVRDevice.h"
 #include "modules/vr/VRController.h"
 #include "modules/vr/VRGetDevicesCallback.h"
 #include "modules/vr/VRHardwareUnit.h"
 #include "modules/vr/VRHardwareUnitCollection.h"
 #include "modules/vr/VRPositionState.h"
 
 namespace blink {
 
 NavigatorVRDevice* NavigatorVRDevice::from(Document& document)
 {
     if (!document.frame() || !document.frame()->domWindow())
-        return 0;
-    Navigator& navigator = *document.frame()->domWindow()->navigator();
-    return &from(navigator);
+        return nullptr;
+    Navigator* navigator = document.frame()->domWindow()->navigator();
+    if (!navigator)
+        return nullptr;
+    return &from(*navigator);
 }
 
 NavigatorVRDevice& NavigatorVRDevice::from(Navigator& navigator)
 {
     NavigatorVRDevice* supplement = static_cast<NavigatorVRDevice*>(HeapSupplement<Navigator>::from(navigator, supplementName()));
     if (!supplement) {
         supplement = new NavigatorVRDevice(navigator.frame());
         provideTo(navigator, supplementName(), supplement);
     }
     return *supplement;
@@ skipping 47 matching lines @@
 NavigatorVRDevice::~NavigatorVRDevice()
 {
 }
 
 const char* NavigatorVRDevice::supplementName()
 {
     return "NavigatorVRDevice";
 }
 
 } // namespace blink