Ensure we don't load plugins on the IO thread

chrome/browser/renderer_host/resource_handler.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This is the browser side of the resource dispatcher, it receives requests
 // from the RenderProcessHosts, and dispatches them to URLRequests. It then
 // fowards the messages from the URLRequests back to the correct process for
 // handling.
 //
 // See http://dev.chromium.org/developers/design-documents/multi-process-resource-loading
@@ skipping 34 matching lines @@
 };
 
 // Simple wrapper that refcounts ResourceResponseHead.
 struct ResourceResponse : public base::RefCounted<ResourceResponse> {
   ResourceResponseHead response_head;
 };
 
 // The resource dispatcher host uses this interface to push load events to the
 // renderer, allowing for differences in the types of IPC messages generated.
 // See the implementations of this interface defined below.
-class ResourceHandler : public base::RefCounted<ResourceHandler> {
+class ResourceHandler : public base::RefCountedThreadSafe<ResourceHandler> {
  public:
   virtual ~ResourceHandler() {}
 
   // Called as upload progress is made.
   virtual bool OnUploadProgress(int request_id,
                                 uint64 position,
                                 uint64 size) {
     return true;
   }
 
@@ skipping 20 matching lines @@
   // Data (*bytes_read bytes) was written into the buffer provided by
   // OnWillRead. A return value of false cancels the request, true continues
   // reading data.
   virtual bool OnReadCompleted(int request_id, int* bytes_read) = 0;
 
   // The response is complete.  The final response status is given.
   // Returns false if the handler is deferring the call to a later time.
   virtual bool OnResponseCompleted(int request_id,
                                    const URLRequestStatus& status,
                                    const std::string& security_info) = 0;
+
+  // Signals that the request is closed (i.e. finished successfully, cancelled).
+  // This is a signal that the associated URLRequest isn't valid anymore.
+  virtual void OnRequestClosed() { }
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_RESOURCE_HANDLER_H_