Simplify ContextLifecycleNotifier's handling of ActiveDOMObjects.

Source/core/dom/ContextLifecycleNotifier.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2013 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 28 matching lines @@
 
 class ContextLifecycleNotifier : public LifecycleNotifier<ExecutionContext, ContextLifecycleObserver> {
 public:
     void addObserver(ContextLifecycleObserver*);
     void removeObserver(ContextLifecycleObserver*);
 
     void notifyResumingActiveDOMObjects();
     void notifySuspendingActiveDOMObjects();
     void notifyStoppingActiveDOMObjects();
 
-    using ActiveDOMObjectSet = HashSet<ActiveDOMObject*>;
-
-    const ActiveDOMObjectSet& activeDOMObjects() const { return m_activeDOMObjects; }
-    bool contains(ActiveDOMObject* object) const { return m_activeDOMObjects.contains(object); }
+    unsigned activeDOMObjectCount() const { return m_activeDOMObjectCount; }

[haraken, 2015/03/03 04:46:21]

This is used only in window.internals to count the number of media objects. We
should directly count up the number of media objects and remove this method (as
you know, windows.internals.activeDOMObjectCount has been a cause to make test
results of encrypted-media tests flaky, because the number of live
ActiveDOMObjects changes as we move more things to Oilpan).

[sof, 2015/03/03 07:26:18]

Agreed, iterating over the set to count them up is preferable as that
testing-internal use is the only one.

Now done.

     bool hasPendingActivity() const;
 
 protected:
     explicit ContextLifecycleNotifier(ExecutionContext*);
 
+#if ENABLE(ASSERT)
+    bool contains(ActiveDOMObject*) const;
+#endif
+
 private:
-    ActiveDOMObjectSet m_activeDOMObjects;
+    unsigned m_activeDOMObjectCount;
 };
 
 } // namespace blink
 
 #endif // ContextLifecycleNotifier_h