Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/sync_host_resolver.h

-// 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.
-
-#ifndef NET_PROXY_SYNC_HOST_RESOLVER_H_
-#define NET_PROXY_SYNC_HOST_RESOLVER_H_
-
-#include "net/base/host_resolver.h"
-#include "net/base/net_export.h"
-
-namespace net {
-
-class BoundNetLog;
-
-// Interface used by ProxyResolverJSBindings to abstract a synchronous host
-// resolver module (which includes a Shutdown method).
-class NET_EXPORT_PRIVATE SyncHostResolver {
- public:
-  virtual ~SyncHostResolver() {}
-
-  virtual int Resolve(const HostResolver::RequestInfo& info,
-                      AddressList* addresses,
-                      const BoundNetLog& net_log) = 0;
-
-  // Optionally aborts any blocking resolves that are in progress.
-  virtual void Shutdown() = 0;
-};
-
-}  // namespace net
-
-#endif  // NET_PROXY_SYNC_HOST_RESOLVER_H_