Revert of Use registerWeakMembers to clean up IntersectionObserver.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/IntersectionObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "core/dom/ExceptionCode.h"
@@ skipping 168 matching lines @@
     }
     if (rootNode->isDocumentNode()) {
         ASSERT(targetDocument == rootNode);
         return true;
     }
     return target->isDescendantOf(rootNode);
 }
 
 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;
     }
     if (!target) {
         exceptionState.throwTypeError("Observation target must be an element.");
         return;
     }
     if (m_root.get() == target) {
         exceptionState.throwDOMException(HierarchyRequestError, "Cannot use the same element for root and target.");
@@ skipping 14 matching lines @@
     if (target->ensureIntersectionObserverData().getObservationFor(*this))
         return;
 
     IntersectionObservation* observation = new IntersectionObservation(*this, *target, shouldReportRootBounds);
     target->ensureIntersectionObserverData().addObservation(*observation);
     m_observations.add(observation);
 }
 
 void IntersectionObserver::unobserve(Element* target, ExceptionState&)
 {
+    checkRootAndDetachIfNeeded();
     if (!target || !target->intersectionObserverData())
         return;
     // TODO(szager): unobserve callback
     if (IntersectionObservation* observation = target->intersectionObserverData()->getObservationFor(*this))
         observation->disconnect();
 }
 
 void IntersectionObserver::computeIntersectionObservations(double timestamp)
 {
+    checkRootAndDetachIfNeeded();
     if (!m_root)
         return;
     for (auto& observation : m_observations)
         observation->computeIntersectionObservations(timestamp);
 }
 
 void IntersectionObserver::disconnect()
 {
     HeapVector<Member<IntersectionObservation>> observationsToDisconnect;
     copyToVector(m_observations, observationsToDisconnect);
     for (auto& observation : observationsToDisconnect)
         observation->disconnect();
     ASSERT(m_observations.isEmpty());
 }
 
 void IntersectionObserver::removeObservation(IntersectionObservation& observation)
 {
     m_observations.remove(&observation);
 }
 
 HeapVector<Member<IntersectionObserverEntry>> IntersectionObserver::takeRecords()
 {
+    checkRootAndDetachIfNeeded();
     HeapVector<Member<IntersectionObserverEntry>> entries;
     entries.swap(m_entries);
     return entries;
 }
 
 void IntersectionObserver::enqueueIntersectionObserverEntry(IntersectionObserverEntry& entry)
 {
     m_entries.append(&entry);
     toDocument(m_callback->executionContext())->ensureIntersectionObserverController().scheduleIntersectionObserverForDelivery(*this);
 }
@@ skipping 24 matching lines @@
 unsigned IntersectionObserver::firstThresholdGreaterThan(float ratio) const
 {
     unsigned result = 0;
     while (result < m_thresholds.size() && m_thresholds[result] < ratio)
         ++result;
     return result;
 }
 
 void IntersectionObserver::deliver()
 {
+    checkRootAndDetachIfNeeded();
+
     if (m_entries.isEmpty())
         return;
 
     HeapVector<Member<IntersectionObserverEntry>> entries;
     entries.swap(m_entries);
     m_callback->handleEvent(entries, *this);
 }
 
 void IntersectionObserver::setActive(bool active)
 {
+    checkRootAndDetachIfNeeded();
     for (auto& observation : m_observations)
         observation->setActive(m_root && active && isDescendantOfRoot(observation->target()));
 }
 
 bool IntersectionObserver::hasPercentMargin() const
 {
     return (m_topMargin.type() == Percent
         || m_rightMargin.type() == Percent
         || m_bottomMargin.type() == Percent
         || m_leftMargin.type() == Percent);
 }
 
-void IntersectionObserver::rootDisappearedCallback(Visitor* visitor, void* self)
+void IntersectionObserver::checkRootAndDetachIfNeeded()
 {
-    IntersectionObserver* observer = static_cast<IntersectionObserver*>(self);
-    observer->disconnect();
+#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();
+#endif
 }
 
 DEFINE_TRACE(IntersectionObserver)
 {
-#if ENABLE(OILPAN)
-    visitor->registerWeakMembers(this, m_root.get(), IntersectionObserver::rootDisappearedCallback);
-#endif
     visitor->trace(m_callback);
     visitor->trace(m_root);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }
 
 } // namespace blink