Oilpan: Prepare moving AXObject to heap

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 54d441b04924514d9f0c227025738fa578d92f9c..87c8416bc5b8a52f0b312fb49d1d27bed743756e 100644
--- a/Source/modules/accessibility/AXScrollbar.cpp
+++ b/Source/modules/accessibility/AXScrollbar.cpp
@@ -48,9 +48,9 @@ void AXScrollbar::detachFromParent()
     AXMockObject::detachFromParent();
 }
 
-PassRefPtr<AXScrollbar> AXScrollbar::create(Scrollbar* scrollbar, AXObjectCacheImpl& axObjectCache)
+PassRefPtrWillBeRawPtr<AXScrollbar> AXScrollbar::create(Scrollbar* scrollbar, AXObjectCacheImpl& axObjectCache)
 {
-    return adoptRef(new AXScrollbar(scrollbar, axObjectCache));
+    return adoptRefWillBeNoop(new AXScrollbar(scrollbar, axObjectCache));
 }
 
 LayoutRect AXScrollbar::elementRect() const
@@ -111,4 +111,10 @@ void AXScrollbar::setValue(float value)
     m_scrollbar->scrollableArea()->setScrollPositionSingleAxis(m_scrollbar->orientation(), newValue, ProgrammaticScroll);
 }
 
+DEFINE_TRACE(AXScrollbar)
+{
+    visitor->trace(m_scrollbar);
+    AXMockObject::trace(visitor);
+}
+
 } // namespace blink