Simplify ContextLifecycleNotifier's handling of ActiveDOMObjects.

Source/core/dom/ContextLifecycleNotifier.h

Index: Source/core/dom/ContextLifecycleNotifier.h
diff --git a/Source/core/dom/ContextLifecycleNotifier.h b/Source/core/dom/ContextLifecycleNotifier.h
index 3a4c914d973973124d58621585e1faf8e4ea69fb..a2a127db89043b5b1d3acce2d43e7fbe237c7469 100644
--- a/Source/core/dom/ContextLifecycleNotifier.h
+++ b/Source/core/dom/ContextLifecycleNotifier.h
@@ -46,17 +46,18 @@ public:
     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