Do not use untraced members while notifying ActiveDOMObjects.

third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h

Index: third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h
diff --git a/third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h b/third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h
index a8d11aafb3ec4ce1dae2ccd4bd33a15d53445cef..3f00b353fdb91bb7358b3ca4e1376ffffb029a24 100644
--- a/third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h
+++ b/third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.h
@@ -58,6 +58,14 @@ protected:
 #if DCHECK_IS_ON()
     bool contains(ActiveDOMObject*) const;
 #endif
+
+private:
+    // Iterates over a snapshot of the observers, invoking the
+    // callback with each observer that is an ActiveDOMObject.
+    // Observers must not be added during |eachActiveDOMObject|. It is
+    // safe to remove observers, though. The callback is not invoked
+    // for observers which get removed first.
+    void eachActiveDOMObject(void (*)(ActiveDOMObject*));
 };
 
 } // namespace blink