Inspector: replace generic discardAgents logic with explicit call to discard a listener.

Source/core/inspector/InspectorDOMAgent.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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.
@@ skipping 83 matching lines @@
 class InspectorDOMAgent : public InspectorBaseAgent<InspectorDOMAgent>, public InspectorBackendDispatcher::DOMCommandHandler {
     WTF_MAKE_NONCOPYABLE(InspectorDOMAgent);
 public:
     struct DOMListener {
         virtual ~DOMListener()
         {
         }
         virtual void didRemoveDocument(Document*) = 0;
         virtual void didRemoveDOMNode(Node*) = 0;
         virtual void didModifyDOMAttr(Element*) = 0;
+        virtual void willDestroyDOMAgent() = 0;
     };
 
     static PassOwnPtr<InspectorDOMAgent> create(InstrumentingAgents* instrumentingAgents, InspectorPageAgent* pageAgent, InspectorCompositeState* inspectorState, InjectedScriptManager* injectedScriptManager, InspectorOverlay* overlay, InspectorClient* client)
     {
         return adoptPtr(new InspectorDOMAgent(instrumentingAgents, pageAgent, inspectorState, injectedScriptManager, overlay, client));
     }
 
     static String toErrorString(const ExceptionCode&);
 
     ~InspectorDOMAgent();
@@ skipping 155 matching lines @@
     OwnPtr<HighlightConfig> m_inspectModeHighlightConfig;
     OwnPtr<InspectorHistory> m_history;
     OwnPtr<DOMEditor> m_domEditor;
     bool m_suppressAttributeModifiedEvent;
 };
 
 
 } // namespace WebCore
 
 #endif // !defined(InspectorDOMAgent_h)