Simplify lifecycle notifiers and observers.

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 178bf676ddc25d37917f03c261bbf2d8a4fd5fb1..3a4c914d973973124d58621585e1faf8e4ea69fb 100644
--- a/Source/core/dom/ContextLifecycleNotifier.h
+++ b/Source/core/dom/ContextLifecycleNotifier.h
@@ -30,26 +30,25 @@
 
 #include "platform/LifecycleNotifier.h"
 #include "wtf/HashSet.h"
-#include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class ActiveDOMObject;
+class ContextLifecycleObserver;
 class ExecutionContext;
 
-class ContextLifecycleNotifier : public LifecycleNotifier<ExecutionContext> {
+class ContextLifecycleNotifier : public LifecycleNotifier<ExecutionContext, ContextLifecycleObserver> {
 public:
-    typedef HashSet<ActiveDOMObject*> ActiveDOMObjectSet;
-
-    const ActiveDOMObjectSet& activeDOMObjects() const { return m_activeDOMObjects; }
-
-    virtual void addObserver(Observer*) override;
-    virtual void removeObserver(Observer*) override;
+    void addObserver(ContextLifecycleObserver*);
+    void removeObserver(ContextLifecycleObserver*);
 
     void notifyResumingActiveDOMObjects();
     void notifySuspendingActiveDOMObjects();
     void notifyStoppingActiveDOMObjects();
 
+    using ActiveDOMObjectSet = HashSet<ActiveDOMObject*>;
+
+    const ActiveDOMObjectSet& activeDOMObjects() const { return m_activeDOMObjects; }

[haraken, 2015/03/01 09:18:39]

Why do we need to keep m_activeDOMObjects while we can remove other hash sets?

[sof, 2015/03/01 10:00:39]

We can remove it also if we accept iterating over the entire set of observers
when evaluating hasPendingActivity() -- there are a number of
non-ActiveDOMObject ExecutionContext observers -- which I didn't feel
comfortable doing right here. We can evaluate doing that in a followup?

[haraken, 2015/03/01 10:47:56]

Sure. Also I'm wondering if a right fix would be to move hasPendingActivity() to
ScriptWrappable because hasPendingActivity() is a way to keep wrappers alive.

[sof, 2015/03/01 17:21:37]

Once this change has proven itself and settled well, more can be done.

     bool contains(ActiveDOMObject* object) const { return m_activeDOMObjects.contains(object); }
     bool hasPendingActivity() const;