Use registerWeakMembers to manage observer root.

third_party/WebKit/Source/core/dom/IntersectionObserver.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
index b29b69e8b46ed857ca07cd7f76d5b958fd182fe6..efe97c99ee3066dda6863f074657f1b085ef15d1 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
@@ -152,6 +152,16 @@ IntersectionObserver::IntersectionObserver(IntersectionObserverCallback& callbac
     root.document().ensureIntersectionObserverController().addTrackedObserver(*this);
 }
 
+#if ENABLE(OILPAN)
+void IntersectionObserver::clearWeakMembers(Visitor* visitor)
+{
+    if (Heap::isHeapObjectAlive(m_root))
+        return;
+    disconnect();
+    m_root = nullptr;
+}
+#endif
+
 LayoutObject* IntersectionObserver::rootLayoutObject() const
 {
     Node* rootNode = root();
@@ -186,7 +196,6 @@ bool IntersectionObserver::isDescendantOfRoot(const Element* target) const
 
 void IntersectionObserver::observe(Element* target, ExceptionState& exceptionState)
 {
-    checkRootAndDetachIfNeeded();
     if (!m_root) {
         exceptionState.throwDOMException(HierarchyRequestError, "Invalid observer: root element or containing document has been deleted.");
         return;
@@ -221,7 +230,6 @@ void IntersectionObserver::observe(Element* target, ExceptionState& exceptionSta
 
 void IntersectionObserver::unobserve(Element* target, ExceptionState&)
 {
-    checkRootAndDetachIfNeeded();
     if (!target || !target->intersectionObserverData())
         return;
     // TODO(szager): unobserve callback
@@ -231,7 +239,6 @@ void IntersectionObserver::unobserve(Element* target, ExceptionState&)
 
 void IntersectionObserver::computeIntersectionObservations(double timestamp)
 {
-    checkRootAndDetachIfNeeded();
     if (!m_root)
         return;
     for (auto& observation : m_observations)
@@ -240,11 +247,9 @@ void IntersectionObserver::computeIntersectionObservations(double timestamp)
 
 void IntersectionObserver::disconnect()
 {
-    HeapVector<Member<IntersectionObservation>> observationsToDisconnect;
-    copyToVector(m_observations, observationsToDisconnect);
-    for (auto& observation : observationsToDisconnect)
-        observation->disconnect();
-    ASSERT(m_observations.isEmpty());
+    for (auto& observation : m_observations)
+        observation->clearRootAndRemoveFromTarget();
+    m_observations.clear();
 }
 
 void IntersectionObserver::removeObservation(IntersectionObservation& observation)
@@ -254,7 +259,6 @@ void IntersectionObserver::removeObservation(IntersectionObservation& observatio
 
 HeapVector<Member<IntersectionObserverEntry>> IntersectionObserver::takeRecords()
 {
-    checkRootAndDetachIfNeeded();
     HeapVector<Member<IntersectionObserverEntry>> entries;
     entries.swap(m_entries);
     return entries;
@@ -299,7 +303,6 @@ unsigned IntersectionObserver::firstThresholdGreaterThan(float ratio) const
 
 void IntersectionObserver::deliver()
 {
-    checkRootAndDetachIfNeeded();
 
     if (m_entries.isEmpty())
         return;
@@ -311,7 +314,6 @@ void IntersectionObserver::deliver()
 
 void IntersectionObserver::setActive(bool active)
 {
-    checkRootAndDetachIfNeeded();
     for (auto& observation : m_observations)
         observation->setActive(m_root && active && isDescendantOfRoot(observation->target()));
 }
@@ -324,27 +326,12 @@ bool IntersectionObserver::hasPercentMargin() const
         || m_leftMargin.type() == Percent);
 }
 
-void IntersectionObserver::checkRootAndDetachIfNeeded()
+DEFINE_TRACE(IntersectionObserver)
 {
 #if ENABLE(OILPAN)
-    // TODO(szager): Pre-oilpan, ElementIntersectionObserverData::dispose() will take
-    // care of this cleanup.  When oilpan ships, there will be a potential leak of the
-    // callback's execution context when the root goes away.  For a detailed explanation:
-    //
-    //   https://goo.gl/PC2Baj
-    //
-    // When that happens, this method should catch most potential leaks, but a complete
-    // solution will still be needed, along the lines described in the above link.
-    if (m_root)
-        return;
-    disconnect();
+    visitor->template registerWeakMembers<IntersectionObserver, &IntersectionObserver::clearWeakMembers>(this);
 #endif
-}
-
-DEFINE_TRACE(IntersectionObserver)
-{
     visitor->trace(m_callback);
-    visitor->trace(m_root);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }