Gracefully support Navigator Gamepad methods in a detached state.

Source/core/frame/DeviceSensorEventController.cpp

Index: Source/core/frame/DeviceSensorEventController.cpp
diff --git a/Source/core/frame/DeviceSensorEventController.cpp b/Source/core/frame/DeviceSensorEventController.cpp
index 912ce1dce9132ba46fd75bf64af4553ec79f4b19..5ffa369be494a6bdd700d4b41f8cc5081b5fb6bf 100644
--- a/Source/core/frame/DeviceSensorEventController.cpp
+++ b/Source/core/frame/DeviceSensorEventController.cpp
@@ -33,10 +33,9 @@
 
 namespace WebCore {
 
-DeviceSensorEventController::DeviceSensorEventController(Document& document)
-    : PageLifecycleObserver(document.page())
+DeviceSensorEventController::DeviceSensorEventController(Page* page)
+    : PageLifecycleObserver(page)
     , m_hasEventListener(false)
-    , m_document(document)
     , m_isActive(false)
     , m_needsCheckingNullEvents(true)
     , m_timer(this, &DeviceSensorEventController::fireDeviceEvent)
@@ -58,11 +57,13 @@ void DeviceSensorEventController::fireDeviceEvent(Timer<DeviceSensorEventControl
 
 void DeviceSensorEventController::dispatchDeviceEvent(PassRefPtrWillBeRawPtr<Event> prpEvent)
 {
-    if (!m_document.domWindow() || m_document.activeDOMObjectsAreSuspended() || m_document.activeDOMObjectsAreStopped())
+    Document* targetDocument = document();
+
+    if (!targetDocument || !targetDocument->domWindow() || targetDocument->activeDOMObjectsAreSuspended() || targetDocument->activeDOMObjectsAreStopped())
         return;
 
     RefPtrWillBeRawPtr<Event> event = prpEvent;
-    m_document.domWindow()->dispatchEvent(event);
+    targetDocument->domWindow()->dispatchEvent(event);
 
     if (m_needsCheckingNullEvents) {
         if (isNullEvent(event.get()))