Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/html/FormAssociatedElement.cpp

Index: Source/core/html/FormAssociatedElement.cpp
diff --git a/Source/core/html/FormAssociatedElement.cpp b/Source/core/html/FormAssociatedElement.cpp
index a34beaacfff356699497c7a6d6e2b5a1f84a626b..46fc8b51335a12c36166786b6ebba8fa67ca7b35 100644
--- a/Source/core/html/FormAssociatedElement.cpp
+++ b/Source/core/html/FormAssociatedElement.cpp
@@ -36,7 +36,7 @@ namespace WebCore {
 
 using namespace HTMLNames;
 
-class FormAttributeTargetObserver : IdTargetObserver {
+class FormAttributeTargetObserver : public IdTargetObserver {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     static PassOwnPtr<FormAttributeTargetObserver> create(const AtomicString& id, FormAssociatedElement*);
@@ -70,7 +70,7 @@ void FormAssociatedElement::didMoveToNewDocument(Document& oldDocument)
 {
     HTMLElement* element = toHTMLElement(this);
     if (element->fastHasAttribute(formAttr))
-        m_formAttributeTargetObserver = nullptr;
+        setFormAttributeTargetObserver(nullptr);
 }
 
 void FormAssociatedElement::insertedInto(ContainerNode* insertionPoint)
@@ -90,7 +90,7 @@ void FormAssociatedElement::removedFrom(ContainerNode* insertionPoint)
 {
     HTMLElement* element = toHTMLElement(this);
     if (insertionPoint->inDocument() && element->fastHasAttribute(formAttr))
-        m_formAttributeTargetObserver = nullptr;
+        setFormAttributeTargetObserver(nullptr);
     // If the form and element are both in the same tree, preserve the connection to the form.
     // Otherwise, null out our form and remove ourselves from the form's list of elements.
     if (m_form && element->highestAncestorOrSelf() != m_form->highestAncestorOrSelf())
@@ -253,14 +253,21 @@ void FormAssociatedElement::setCustomValidity(const String& error)
     m_customValidationMessage = error;
 }
 
+void FormAssociatedElement::setFormAttributeTargetObserver(PassOwnPtr<FormAttributeTargetObserver> newObserver)

[haraken, 2014/05/06 15:59:42]

This complexity will be removed once we move IdTargetObserver to the heap and
implement weak processing for the observer set.

[Mads Ager (chromium), 2014/05/07 12:13:16]

Yes, if that is the right thing to do. It will make the unregistration depend on
GC which it currently doesn't. With these changes, the unregistration happens
with explicit notifications and therefore matches what happened pre-oilpan.

+{
+    if (m_formAttributeTargetObserver)
+        m_formAttributeTargetObserver->unregister();
+    m_formAttributeTargetObserver = newObserver;
+}
+
 void FormAssociatedElement::resetFormAttributeTargetObserver()
 {
     HTMLElement* element = toHTMLElement(this);
     const AtomicString& formId(element->fastGetAttribute(formAttr));
     if (!formId.isNull() && element->inDocument())
-        m_formAttributeTargetObserver = FormAttributeTargetObserver::create(formId, this);
+        setFormAttributeTargetObserver(FormAttributeTargetObserver::create(formId, this));
     else
-        m_formAttributeTargetObserver = nullptr;
+        setFormAttributeTargetObserver(nullptr);
 }
 
 void FormAssociatedElement::formAttributeTargetChanged()