Oilpan: support observer retirement during lifetime notifications.

Source/core/dom/DocumentLifecycleNotifier.cpp

Index: Source/core/dom/DocumentLifecycleNotifier.cpp
diff --git a/Source/core/dom/DocumentLifecycleNotifier.cpp b/Source/core/dom/DocumentLifecycleNotifier.cpp
index 12fc7db522b4032cb733342f5e647fd83d44e211..e9b8cd042145c6f8abbc3c6176493f1b4c09d342 100644
--- a/Source/core/dom/DocumentLifecycleNotifier.cpp
+++ b/Source/core/dom/DocumentLifecycleNotifier.cpp
@@ -34,16 +34,39 @@ namespace blink {
 void DocumentLifecycleNotifier::notifyDocumentWasDetached()
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
+#if !ENABLE(OILPAN)
+    // Notifications perform unknown amounts of heap allocations,
+    // which might trigger (conservative) GCs. This will flush out
+    // dead observers, causing the _non-heap_ set be updated. Snapshot
+    // the observers and explicitly check if they're still alive before
+    // notifying.
+    Vector<RawPtr<DocumentLifecycleObserver>> snapshotOfObservers;
+    copyToVector(m_observers, snapshotOfObservers);
+    for (DocumentLifecycleObserver* observer : snapshotOfObservers) {
+        if (m_observers.contains(observer))
+            observer->documentWasDetached();
+    }
+#else
     for (DocumentLifecycleObserver* observer : m_observers)
         observer->documentWasDetached();
+#endif
 }
 
 #if !ENABLE(OILPAN)
 void DocumentLifecycleNotifier::notifyDocumentWasDisposed()
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
-    for (DocumentLifecycleObserver* observer : m_observers)
-        observer->documentWasDisposed();
+    // Notifications perform unknown amounts of heap allocations,
+    // which might trigger (conservative) GCs. This will flush out
+    // dead observers, causing the _non-heap_ set be updated. Snapshot
+    // the observers and explicitly check if they're still alive before
+    // notifying.
+    Vector<RawPtr<DocumentLifecycleObserver>> snapshotOfObservers;
+    copyToVector(m_observers, snapshotOfObservers);
+    for (DocumentLifecycleObserver* observer : snapshotOfObservers) {
+        if (m_observers.contains(observer))
+            observer->documentWasDisposed();
+    }
 }
 #endif