Oilpan: Prepare moving AXObject to heap

Source/modules/accessibility/AXMenuListOption.cpp

 /*
  * Copyright (C) 2010 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 21 matching lines @@
 namespace blink {
 
 using namespace HTMLNames;
 
 AXMenuListOption::AXMenuListOption(HTMLOptionElement* element, AXObjectCacheImpl& axObjectCache)
     : AXMockObject(axObjectCache)
     , m_element(element)
 {
 }
 
+AXMenuListOption::~AXMenuListOption()
+{
+    ASSERT(!m_element);
+}
+
 void AXMenuListOption::detach()
 {
     m_element = nullptr;
     AXMockObject::detach();
 }
 
 Element* AXMenuListOption::actionElement() const
 {
     return m_element;
 }
 
 bool AXMenuListOption::isEnabled() const
 {
     // isDisabledFormControl() returns true if the parent <select> element is disabled,
     // which we don't want.
-    return !m_element->ownElementDisabled();
+    return m_element && !m_element->ownElementDisabled();
 }
 
 bool AXMenuListOption::isVisible() const
 {
     if (!m_parent)
         return false;
 
     // In a single-option select with the popup collapsed, only the selected
     // item is considered visible.
     return !m_parent->isOffScreen() || isSelected();
 }
 
 bool AXMenuListOption::isOffScreen() const
 {
     // Invisible list options are considered to be offscreen.
     return !isVisible();
 }
 
 bool AXMenuListOption::isSelected() const
 {
     AXMenuListPopup* parent = static_cast<AXMenuListPopup*>(parentObject());
     if (parent && !parent->isOffScreen())
         return parent->activeChild() == this;
-    return m_element->selected();
+    return m_element && m_element->selected();
 }
 
 void AXMenuListOption::setSelected(bool b)
 {
-    if (!canSetSelectedAttribute())
+    if (!m_element || !canSetSelectedAttribute())
         return;
 
     m_element->setSelected(b);
 }
 
 bool AXMenuListOption::canSetSelectedAttribute() const
 {
     return isEnabled();
 }
 
@@ skipping 12 matching lines @@
     AXObject* grandparent = parent->parentObject();
     if (!grandparent)
         return LayoutRect();
     ASSERT(grandparent->isMenuList());
 
     return grandparent->elementRect();
 }
 
 String AXMenuListOption::stringValue() const
 {
-    return m_element->text();
+    return m_element ? m_element->text() : String();
+}
+
+DEFINE_TRACE(AXMenuListOption)
+{
+    visitor->trace(m_element);
+    AXMockObject::trace(visitor);
 }
 
 } // namespace blink