Use TaskRunner passed in to URLRequestContextBuilder only for the cache

headless/lib/browser/headless_url_request_context_getter.h

 // Copyright 2015 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 HEADLESS_LIB_BROWSER_HEADLESS_URL_REQUEST_CONTEXT_GETTER_H_
 #define HEADLESS_LIB_BROWSER_HEADLESS_URL_REQUEST_CONTEXT_GETTER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 35 matching lines @@
   scoped_refptr<base::SingleThreadTaskRunner> GetNetworkTaskRunner()
       const override;
 
   net::HostResolver* host_resolver() const;
 
  protected:
   ~HeadlessURLRequestContextGetter() override;
 
  private:
   scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
-  // TODO(eseckler): This should become a SequencedTaskRunner once net:: APIs
-  // accept a SequencedTaskRunner, see https://crbug.com/735368.
-  scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
 
   // The |options| object given to the constructor is not guaranteed to outlive
   // this class, so we make copies of the parts we need to access on the IO
   // thread.
   std::string user_agent_;
   std::string host_resolver_rules_;
   const net::ProxyConfig* proxy_config_;  // Not owned.
 
   std::unique_ptr<net::ProxyConfigService> proxy_config_service_;
   std::unique_ptr<net::URLRequestContext> url_request_context_;
   content::ProtocolHandlerMap protocol_handlers_;
   content::URLRequestInterceptorScopedVector request_interceptors_;
   net::NetLog* net_log_;                                  // Not owned.
   HeadlessBrowserContextImpl* headless_browser_context_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessURLRequestContextGetter);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_LIB_BROWSER_HEADLESS_URL_REQUEST_CONTEXT_GETTER_H_