More header cleanup:

net/base/host_resolver_impl.cc

 // Copyright (c) 2010 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.
 
 #include "net/base/host_resolver_impl.h"
 
 #if defined(OS_WIN)
 #include <Winsock2.h>
 #elif defined(OS_POSIX)
 #include <netdb.h>
 #endif
 
 #include <cmath>
 #include <deque>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/debug_util.h"
+#include "base/histogram.h"
 #include "base/lock.h"
 #include "base/message_loop.h"
 #include "base/stl_util-inl.h"
 #include "base/string_util.h"
 #include "base/time.h"
 #include "base/values.h"
 #include "base/worker_pool.h"
 #include "net/base/address_list.h"
 #include "net/base/host_resolver_proc.h"
 #include "net/base/net_log.h"
@@ skipping 1118 matching lines @@
     if (r == req)
       return error;
 
     r->OnComplete(error, AddressList());
   }
 
   return ERR_IO_PENDING;
 }
 
 }  // namespace net