Gracefully support Navigator Gamepad methods in a detached state.

Source/core/frame/DeviceSensorEventController.h

 /*
  * Copyright (C) 2013 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
@@ skipping 23 matching lines @@
 
 class Document;
 
 class DeviceSensorEventController : public PageLifecycleObserver {
 
 public:
     void startUpdating();
     void stopUpdating();
 
 protected:
-    explicit DeviceSensorEventController(Document&);
+    explicit DeviceSensorEventController(Document*);
     virtual ~DeviceSensorEventController();
 
     void dispatchDeviceEvent(const PassRefPtrWillBeRawPtr<Event>);
 
     virtual bool hasLastData() = 0;
     virtual PassRefPtrWillBeRawPtr<Event> getLastEvent() = 0;
     virtual void registerWithDispatcher() = 0;
     virtual void unregisterWithDispatcher() = 0;
     virtual bool isNullEvent(Event*) = 0;
 
     bool m_hasEventListener;
 
 private:
     // Inherited from PageLifecycleObserver.
     virtual void pageVisibilityChanged() OVERRIDE FINAL;
 
     void fireDeviceEvent(Timer<DeviceSensorEventController>*);
 
-    Document& m_document;
+    // Will be null if created in a detached state, without
+    // a frame (and its document.)
+    Document* m_document;

[abarth-chromium, 2014/04/28 17:58:14]

Maybe rather than storing this pointer, this class should get its document from
an abstract virtual function?  It looks like folks use this class by subclassing
and each have different ways of watching for the document's destruction.

[sof, 2014/04/28 18:58:42]

Thanks, I like that suggestion, will try to make it work out.

     bool m_isActive;
     bool m_needsCheckingNullEvents;
     Timer<DeviceSensorEventController> m_timer;
 };
 
 } // namespace WebCore
 
 #endif // DeviceSensorEventController_h