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

Source/modules/gamepad/NavigatorGamepad.cpp

 /*
  * Copyright (C) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 55 matching lines @@
             into->set(i, gamepad);
         } else {
             into->set(i, 0);
         }
     }
 }
 
 NavigatorGamepad* NavigatorGamepad::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);
 }
 
 NavigatorGamepad& NavigatorGamepad::from(Navigator& navigator)
 {
     NavigatorGamepad* supplement = static_cast<NavigatorGamepad*>(HeapSupplement<Navigator>::from(navigator, supplementName()));
     if (!supplement) {
         supplement = new NavigatorGamepad(navigator.frame());
         provideTo(navigator, supplementName(), supplement);
     }
     return *supplement;
@@ skipping 190 matching lines @@
         if (connectedGamepadChanged || (!oldWasConnected && newIsConnected)) {
             m_pendingEvents.append(newGamepad);
         }
     }
 
     if (!m_pendingEvents.isEmpty())
         m_dispatchOneEventRunner.runAsync();
 }
 
 } // namespace blink