Oilpan: support observer retirement during lifetime notifications.

Source/core/frame/LocalFrameLifecycleNotifier.cpp

Index: Source/core/frame/LocalFrameLifecycleNotifier.cpp
diff --git a/Source/core/frame/LocalFrameLifecycleNotifier.cpp b/Source/core/frame/LocalFrameLifecycleNotifier.cpp
index 434cf8bc2c36ffdc0ddd766b23b124726e87aeca..828226710e1ae5ba7d5b04073d453d4b1c2eb811 100644
--- a/Source/core/frame/LocalFrameLifecycleNotifier.cpp
+++ b/Source/core/frame/LocalFrameLifecycleNotifier.cpp
@@ -12,8 +12,22 @@ namespace blink {
 void LocalFrameLifecycleNotifier::notifyWillDetachFrameHost()
 {
     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<LocalFrameLifecycleObserver>> snapshotOfObservers;
+    copyToVector(m_observers, snapshotOfObservers);
+    for (LocalFrameLifecycleObserver* observer : snapshotOfObservers) {
+        if (m_observers.contains(observer))
+            observer->willDetachFrameHost();
+    }
+#else
     for (LocalFrameLifecycleObserver* observer : m_observers)
         observer->willDetachFrameHost();
+#endif
 }
 
 } // namespace blink