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

Source/core/inspector/InspectorDOMAgent.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * 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
@@ skipping 220 matching lines @@
     , m_domListener(0)
     , m_lastNodeId(1)
     , m_lastBackendNodeId(-1)
     , m_searchingForNode(false)
     , m_suppressAttributeModifiedEvent(false)
 {
 }
 
 InspectorDOMAgent::~InspectorDOMAgent()
 {
+    if (m_domListener)
+        m_domListener->willDestroyDOMAgent();
     reset();
     ASSERT(!m_searchingForNode);
 }
 
 void InspectorDOMAgent::setFrontend(InspectorFrontend* frontend)
 {
     ASSERT(!m_frontend);
     m_history = adoptPtr(new InspectorHistory());
     m_domEditor = adoptPtr(new DOMEditor(m_history.get()));
 
@@ skipping 1575 matching lines @@
 
     InjectedScript injectedScript = m_injectedScriptManager->injectedScriptFor(mainWorldScriptState(frame));
     if (injectedScript.hasNoValue())
         return 0;
 
     return injectedScript.wrapNode(node, objectGroup);
 }
 
 } // namespace WebCore