Add a Dns preresolve interface in //content

net/dns/single_request_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_DNS_SINGLE_REQUEST_HOST_RESOLVER_H_
 #define NET_DNS_SINGLE_REQUEST_HOST_RESOLVER_H_
 
 #include "base/macros.h"
 #include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
@@ skipping 13 matching lines @@
   // |resolver| must remain valid for the lifetime of |this|.
   explicit SingleRequestHostResolver(HostResolver* resolver);
 
   // If a completion callback is pending when the resolver is destroyed, the
   // host resolution is cancelled, and the completion callback will not be
   // called.
   ~SingleRequestHostResolver();
 
   // Resolves the given hostname (or IP address literal), filling out the
   // |addresses| object upon success. See HostResolver::Resolve() for details.
+  // Note, |addresses| can be null if the caller does not care about the return
+  // resolution result, and only wishes to perform the resolution.
   int Resolve(const HostResolver::RequestInfo& info,
               RequestPriority priority,
               AddressList* addresses,
               const CompletionCallback& callback,
               const BoundNetLog& net_log);
 
   // Cancels the in-progress request, if any. This prevents the callback
   // from being invoked. Resolve() can be called again after cancelling.
   void Cancel();
 
  private:
   // Callback for when the request to |resolver_| completes, so we dispatch
   // to the user's callback.
   void OnResolveCompletion(int result);
 
   // The actual host resolver that will handle the request.
   HostResolver* const resolver_;
 
   // The current request (if any).
   HostResolver::RequestHandle cur_request_;
   CompletionCallback cur_request_callback_;
 
   // Completion callback for when request to |resolver_| completes.
   CompletionCallback callback_;
 
+  std::unique_ptr<AddressList> default_addresses_;
+
   DISALLOW_COPY_AND_ASSIGN(SingleRequestHostResolver);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_SINGLE_REQUEST_HOST_RESOLVER_H_