Avoid issuing a Read() after draining a request.

content/browser/loader/resource_handler.h

 // Copyright (c) 2012 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 79 matching lines @@
   // If the handler returns false, then the request is cancelled.  Otherwise,
   // once data is available, OnReadCompleted will be called.
   virtual bool OnWillRead(int request_id,
                           scoped_refptr<net::IOBuffer>* buf,
                           int* buf_size,
                           int min_size) = 0;
 
   // Data (*bytes_read bytes) was written into the buffer provided by
   // OnWillRead.  A return value of false cancels the request, true continues
   // reading data.  Set |*defer| to true to defer reading more response data.
-  // Call controller()->Resume() to continue reading response data.
+  // Call controller()->Resume() to continue reading response data.  A zero
+  // |bytes_read| signals that no further data is available.
   virtual bool OnReadCompleted(int request_id, int bytes_read,
                                bool* defer) = 0;
 
   // The response is complete.  The final response status is given.  Set
   // |*defer| to true to defer destruction to a later time.  Otherwise, the
   // request will be destroyed upon return.
   virtual void OnResponseCompleted(int request_id,
                                    const net::URLRequestStatus& status,
                                    const std::string& security_info,
                                    bool* defer) = 0;
@@ skipping 16 matching lines @@
   ResourceMessageFilter* GetFilter() const;
 
  private:
   ResourceController* controller_;
   net::URLRequest* request_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_RESOURCE_HANDLER_H_