[WIP]Oilpan: checking for nearly-dead observers.

Source/core/frame/LocalFrameLifecycleNotifier.cpp

 // Copyright 2015 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 "config.h"
 #include "core/frame/LocalFrameLifecycleNotifier.h"
 
 #include "core/frame/LocalFrameLifecycleObserver.h"
 
 namespace blink {
 
 void LocalFrameLifecycleNotifier::notifyWillDetachFrameHost()
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
-    for (LocalFrameLifecycleObserver* observer : m_observers)
+    for (LocalFrameLifecycleObserver* observer : m_observers) {
+#if !ENABLE(OILPAN)
+        if (!isObserverAlive(observer))
+            continue;
+#endif
         observer->willDetachFrameHost();
+    }
 }
 
 } // namespace blink