net: Cleanup class/struct forward declarations

net/proxy/mojo_proxy_resolver_factory_impl.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 NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_
 #define NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_
 
 #include <map>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "net/interfaces/proxy_resolver_service.mojom.h"
 
 namespace net {
-class HostResolver;
-class ProxyResolverErrorObserver;
 class ProxyResolverV8TracingFactory;
 
 class MojoProxyResolverFactoryImpl : public interfaces::ProxyResolverFactory {
  public:
   MojoProxyResolverFactoryImpl();
   explicit MojoProxyResolverFactoryImpl(
       std::unique_ptr<ProxyResolverV8TracingFactory> proxy_resolver_factory);
 
   ~MojoProxyResolverFactoryImpl() override;
 
@@ skipping 12 matching lines @@
       proxy_resolver_impl_factory_;
 
   std::map<Job*, std::unique_ptr<Job>> jobs_;
 
   DISALLOW_COPY_AND_ASSIGN(MojoProxyResolverFactoryImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_