Refactor: Clear m_axObjectCache when AXObject detaches

Source/modules/accessibility/AXScrollbar.cpp

Index: Source/modules/accessibility/AXScrollbar.cpp
diff --git a/Source/modules/accessibility/AXScrollbar.cpp b/Source/modules/accessibility/AXScrollbar.cpp
index 778ff9498de785866c63d6d16fe75c528fbd55c7..54d441b04924514d9f0c227025738fa578d92f9c 100644
--- a/Source/modules/accessibility/AXScrollbar.cpp
+++ b/Source/modules/accessibility/AXScrollbar.cpp
@@ -35,7 +35,7 @@
 
 namespace blink {
 
-AXScrollbar::AXScrollbar(Scrollbar* scrollbar, AXObjectCacheImpl* axObjectCache)
+AXScrollbar::AXScrollbar(Scrollbar* scrollbar, AXObjectCacheImpl& axObjectCache)
     : AXMockObject(axObjectCache)
     , m_scrollbar(scrollbar)
 {
@@ -48,7 +48,7 @@ void AXScrollbar::detachFromParent()
     AXMockObject::detachFromParent();
 }
 
-PassRefPtr<AXScrollbar> AXScrollbar::create(Scrollbar* scrollbar, AXObjectCacheImpl* axObjectCache)
+PassRefPtr<AXScrollbar> AXScrollbar::create(Scrollbar* scrollbar, AXObjectCacheImpl& axObjectCache)
 {
     return adoptRef(new AXScrollbar(scrollbar, axObjectCache));
 }