[net] Better StopCaching() handling for HttpCache::Transaction.

net/http/http_transaction.h

 // Copyright (c) 2011 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.
 
 #ifndef NET_HTTP_HTTP_TRANSACTION_H_
 #define NET_HTTP_HTTP_TRANSACTION_H_
 
 #include <stdint.h>
 
 #include "net/base/completion_callback.h"
@@ skipping 94 matching lines @@
   // the error.  Any other negative return value indicates that the transaction
   // could not be read.
   //
   // NOTE: The transaction is not responsible for deleting the callback object.
   // If the operation is not completed immediately, the transaction must acquire
   // a reference to the provided buffer.
   //
   virtual int Read(IOBuffer* buf, int buf_len,
                    const CompletionCallback& callback) = 0;
 
-  // Stops further caching of this request by the HTTP cache, if there is any.
+  // Stops further caching of this request by the HTTP cache.
+  //
+  // Only valid if called after Start() and only when there are no pending
+  // operations.
   virtual void StopCaching() = 0;
 
   // Gets the full request headers sent to the server.  This is guaranteed to
   // work only if Start returns success and the underlying transaction supports
   // it.  (Right now, this is only network transactions, not cache ones.)
   //
   // Returns true and overwrites headers if it can get the request headers;
   // otherwise, returns false and does not modify headers.
   virtual bool GetFullRequestHeaders(HttpRequestHeaders* headers) const = 0;
 
@@ skipping 54 matching lines @@
 
   // Resumes the transaction after being deferred.
   virtual int ResumeNetworkStart() = 0;
 
   virtual void GetConnectionAttempts(ConnectionAttempts* out) const = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_TRANSACTION_H_