Clean up dns prefetch code, and also port it.

net/base/host_resolver.h

 // Copyright (c) 2006-2008 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_HOST_RESOLVER_H_
 #define NET_BASE_HOST_RESOLVER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 23 matching lines @@
   // called.
   ~HostResolver();
 
   // Resolves the given hostname (or IP address literal), filling out the
   // |addresses| object upon success.  The |port| parameter will be set as the
   // sin(6)_port field of the sockaddr_in{6} struct.  Returns OK if successful
   // or an error code upon failure.
   //
   // When callback is null, the operation completes synchronously.
   //
-  // When callback is non-null, ERR_IO_PENDING is returned if the operation
-  // could not be completed synchronously, in which case the result code will
-  // be passed to the callback when available.
-  //
+  // When callback is non-null, the operation will be performed asynchronously.
+  // ERR_IO_PENDING is returned if it has been scheduled successfully. Real
+  // result code will be passed to the completion callback.
   int Resolve(const std::string& hostname, int port,
               AddressList* addresses, CompletionCallback* callback);
 
  private:
   class Request;
   friend class Request;
   scoped_refptr<Request> request_;
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };
 
@@ skipping 31 matching lines @@
 //
 // NOTE: In most cases, you should use ScopedHostMapper instead, which is
 // defined in host_resolver_unittest.h
 //
 HostMapper* SetHostMapper(HostMapper* host_mapper);
 #endif
 
 }  // namespace net
 
 #endif  // NET_BASE_HOST_RESOLVER_H_