Add an explicit dispose step for WebDevToolsAgentImpl.

Source/web/WebDevToolsAgentImpl.h

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 57 matching lines @@
     , public InspectorOverlay::Client
     , public InspectorPageAgent::Client
     , public InspectorTracingAgent::Client
     , public PageRuntimeAgent::Client
     , public InspectorFrontendChannel
     , public WebPageOverlay
     , private WebThread::TaskObserver {
 public:
     WebDevToolsAgentImpl(WebViewImpl*, WebDevToolsAgentClient*);
     ~WebDevToolsAgentImpl() override;
+    void dispose();
     DECLARE_VIRTUAL_TRACE();
 
     void willBeDestroyed();
     WebDevToolsAgentClient* client() { return m_client; }
     bool handleInputEvent(Page*, const WebInputEvent&);
     void flushPendingProtocolNotifications();
     void dispatchMessageFromFrontend(const String& message);
 
     // Instrumentation from web/ layer.
     void didCommitLoadForLocalFrame(LocalFrame*);
@@ skipping 69 matching lines @@
     void enableMobileEmulation();
     void disableMobileEmulation();
     bool handleGestureEvent(LocalFrame*, const PlatformGestureEvent&);
     bool handleMouseEvent(LocalFrame*, const PlatformMouseEvent&);
     bool handleTouchEvent(LocalFrame*, const PlatformTouchEvent&);
     bool handleKeyboardEvent(LocalFrame*, const PlatformKeyboardEvent&);
 
     WebDevToolsAgentClient* m_client;
     WebViewImpl* m_webViewImpl;
     bool m_attached;
+#if ENABLE(ASSERT)
+    bool m_hasBeenDisposed;
+#endif
 
     RefPtrWillBeMember<InstrumentingAgents> m_instrumentingAgents;
     OwnPtrWillBeMember<InjectedScriptManager> m_injectedScriptManager;
     OwnPtrWillBeMember<InspectorCompositeState> m_state;
     OwnPtrWillBeMember<InspectorOverlay> m_overlay;
     OwnPtrWillBeMember<AsyncCallTracker> m_asyncCallTracker;
 
     RawPtrWillBeMember<InspectorDOMAgent> m_domAgent;
     RawPtrWillBeMember<InspectorPageAgent> m_pageAgent;
     RawPtrWillBeMember<InspectorCSSAgent> m_cssAgent;
@@ skipping 21 matching lines @@
     typedef Vector<RefPtr<JSONObject> > NotificationQueue;
     NotificationQueue m_notificationQueue;
     String m_stateCookie;
 
     friend class DebuggerTask;
 };
 
 } // namespace blink
 
 #endif