Gracefully support Navigator Gamepad methods in a detached state.

Source/modules/battery/BatteryManager.cpp

Index: Source/modules/battery/BatteryManager.cpp
diff --git a/Source/modules/battery/BatteryManager.cpp b/Source/modules/battery/BatteryManager.cpp
index 382eff3e7acb7228c2905a062eb3876b7f6317f9..6c2e2b5a633585f16f9207d445486cfd17026712 100644
--- a/Source/modules/battery/BatteryManager.cpp
+++ b/Source/modules/battery/BatteryManager.cpp
@@ -26,7 +26,7 @@ BatteryManager::~BatteryManager()
 
 BatteryManager::BatteryManager(ExecutionContext* context)
     : ActiveDOMObject(context)
-    , DeviceSensorEventController(*toDocument(context))
+    , DeviceSensorEventController(toDocument(context)->page())
 {
     m_hasEventListener = true;
     startUpdating();
@@ -97,6 +97,11 @@ bool BatteryManager::isNullEvent(Event*)
     return false;
 }
 
+Document* BatteryManager::document()
+{
+    return toDocument(executionContext());
+}
+
 void BatteryManager::suspend()
 {
     m_hasEventListener = false;