Oilpan: Prepare moving AXObject to heap

Source/modules/accessibility/AXSpinButton.cpp

Index: Source/modules/accessibility/AXSpinButton.cpp
diff --git a/Source/modules/accessibility/AXSpinButton.cpp b/Source/modules/accessibility/AXSpinButton.cpp
index ed9e3b339b2902ad56c61f99a009c03c91e38bb3..e97dc8e14b63103827f7aa355f758eafaa9695bc 100644
--- a/Source/modules/accessibility/AXSpinButton.cpp
+++ b/Source/modules/accessibility/AXSpinButton.cpp
@@ -31,19 +31,26 @@
 
 namespace blink {
 
-PassRefPtr<AXSpinButton> AXSpinButton::create(AXObjectCacheImpl& axObjectCache)
+PassRefPtrWillBeRawPtr<AXSpinButton> AXSpinButton::create(AXObjectCacheImpl& axObjectCache)
 {
-    return adoptRef(new AXSpinButton(axObjectCache));
+    return adoptRefWillBeNoop(new AXSpinButton(axObjectCache));
 }
 
 AXSpinButton::AXSpinButton(AXObjectCacheImpl& axObjectCache)
     : AXMockObject(axObjectCache)
-    , m_spinButtonElement(0)
+    , m_spinButtonElement(nullptr)
 {
 }
 
 AXSpinButton::~AXSpinButton()
 {
+    ASSERT(!m_spinButtonElement);
+}
+
+DEFINE_TRACE(AXSpinButton)
+{
+    visitor->trace(m_spinButtonElement);
+    AXMockObject::trace(visitor);
 }
 
 LayoutRect AXSpinButton::elementRect() const
@@ -57,13 +64,13 @@ LayoutRect AXSpinButton::elementRect() const
 void AXSpinButton::detach()
 {
     AXObject::detach();
-    m_spinButtonElement = 0;
+    m_spinButtonElement = nullptr;
 }
 
 void AXSpinButton::detachFromParent()
 {
     AXObject::detachFromParent();
-    m_spinButtonElement = 0;
+    m_spinButtonElement = nullptr;
 }
 
 AccessibilityRole AXSpinButton::roleValue() const
@@ -103,9 +110,9 @@ AXSpinButtonPart::AXSpinButtonPart(AXObjectCacheImpl& axObjectCache)
 {
 }
 
-PassRefPtr<AXSpinButtonPart> AXSpinButtonPart::create(AXObjectCacheImpl& axObjectCache)
+PassRefPtrWillBeRawPtr<AXSpinButtonPart> AXSpinButtonPart::create(AXObjectCacheImpl& axObjectCache)
 {
-    return adoptRef(new AXSpinButtonPart(axObjectCache));
+    return adoptRefWillBeNoop(new AXSpinButtonPart(axObjectCache));
 }
 
 LayoutRect AXSpinButtonPart::elementRect() const