Allow ProxyConfigService to report "no configuration set"

net/proxy/polling_proxy_config_service.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_PROXY_POLLING_PROXY_CONFIG_SERVICE_H_
 #define NET_PROXY_POLLING_PROXY_CONFIG_SERVICE_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/time.h"
 #include "net/proxy/proxy_config_service.h"
 
 namespace net {
 
 // PollingProxyConfigService is a base class for creating ProxyConfigService
 // implementations that use polling to notice when settings have change.
 //
 // It runs code to get the current proxy settings on a background worker
 // thread, and notifies registered observers when the value changes.
 class PollingProxyConfigService : public ProxyConfigService {
  public:
   // ProxyConfigService implementation:
   virtual void AddObserver(Observer* observer);
   virtual void RemoveObserver(Observer* observer);
-  virtual bool GetLatestProxyConfig(ProxyConfig* config);
+  virtual ConfigAvailability GetLatestProxyConfig(ProxyConfig* config);
   virtual void OnLazyPoll();
 
  protected:
   // Function for retrieving the current proxy configuration.
   // Implementors must be threadsafe as the function will be invoked from
   // worker threads.
   typedef void (*GetConfigFunction)(ProxyConfig*);
 
   // Creates a polling-based ProxyConfigService which will test for new
   // settings at most every |poll_interval| time by calling |get_config_func|
   // on a worker thread.
   PollingProxyConfigService(
       base::TimeDelta poll_interval,
       GetConfigFunction get_config_func);
 
   virtual ~PollingProxyConfigService();
 
   // Polls for changes by posting a task to the worker pool.
   void CheckForChangesNow();
 
  private:
   class Core;
   scoped_refptr<Core> core_;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_POLLING_PROXY_CONFIG_SERVICE_H_