Remove unused HostResolver::Observer.

net/base/mapped_host_resolver.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_BASE_MAPPED_HOST_RESOLVER_H_
 #define NET_BASE_MAPPED_HOST_RESOLVER_H_
 #pragma once
 
 #include <string>
 
@@ skipping 35 matching lines @@
   // HostResolver methods:
   virtual int Resolve(const RequestInfo& info,
                       AddressList* addresses,
                       OldCompletionCallback* callback,
                       RequestHandle* out_req,
                       const BoundNetLog& net_log) OVERRIDE;
   virtual int ResolveFromCache(const RequestInfo& info,
                                AddressList* addresses,
                                const BoundNetLog& net_log) OVERRIDE;
   virtual void CancelRequest(RequestHandle req) OVERRIDE;
-  virtual void AddObserver(Observer* observer) OVERRIDE;
-  virtual void RemoveObserver(Observer* observer) OVERRIDE;
   virtual void ProbeIPv6Support() OVERRIDE;
   virtual HostCache* GetHostCache() OVERRIDE;
 
  private:
   scoped_ptr<HostResolver> impl_;
 
   HostMappingRules rules_;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_MAPPED_HOST_RESOLVER_H_