Do not call GenerateCacheKey() if disk cache is disabled.

net/http/http_cache.cc

 // 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.
 
 #include "net/http/http_cache.h"
 
 #include <algorithm>
 
 #include "base/compiler_specific.h"
 
@@ skipping 585 matching lines @@
 }
 
 void HttpCache::CloseIdleConnections() {
   HttpNetworkSession* session = GetSession();
   if (session)
     session->CloseIdleConnections();
 }
 
 void HttpCache::OnExternalCacheHit(const GURL& url,
                                    const std::string& http_method) {
-  if (!disk_cache_.get())
+  if (!disk_cache_.get() || mode_ == DISABLE)
     return;
 
   HttpRequestInfo request_info;
   request_info.url = url;
   request_info.method = http_method;
   std::string key = GenerateCacheKey(&request_info);
   disk_cache_->OnExternalCacheHit(key);
 }
 
 void HttpCache::InitializeInfiniteCache(const base::FilePath& path) {
@@ skipping 789 matching lines @@
     building_backend_ = false;
     DeletePendingOp(pending_op);
   }
 
   // The cache may be gone when we return from the callback.
   if (!item->DoCallback(result, disk_cache_.get()))
     item->NotifyTransaction(result, NULL);
 }
 
 }  // namespace net