Gracefully support Navigator Gamepad methods in a detached state.

Source/core/frame/DeviceSensorEventController.h

Index: Source/core/frame/DeviceSensorEventController.h
diff --git a/Source/core/frame/DeviceSensorEventController.h b/Source/core/frame/DeviceSensorEventController.h
index 085f1e2a1c71b79e0d7aa6e248347f329eec47e9..dc4ac0bcfa63635e31b8f75122b6737bdb4aad8d 100644
--- a/Source/core/frame/DeviceSensorEventController.h
+++ b/Source/core/frame/DeviceSensorEventController.h
@@ -41,7 +41,7 @@ public:
     void stopUpdating();
 
 protected:
-    explicit DeviceSensorEventController(Document&);
+    explicit DeviceSensorEventController(Document*);
     virtual ~DeviceSensorEventController();
 
     void dispatchDeviceEvent(const PassRefPtrWillBeRawPtr<Event>);
@@ -60,7 +60,9 @@ private:
 
     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;