Fix android build error with gcc 4.7.2

tools/android/forwarder2/socket.cc

 // 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.
 
 #include "tools/android/forwarder2/socket.h"
 
 #include <arpa/inet.h>
 #include <fcntl.h>
 #include <netdb.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/types.h>
+#include <unistd.h>
 
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/safe_strerror_posix.h"
 #include "tools/android/common/net.h"
 #include "tools/android/forwarder2/common.h"
 
 namespace {
 const int kNoTimeout = -1;
 const int kConnectTimeOut = 10;  // Seconds.
@@ skipping 354 matching lines @@
   return true;
 }
 
 // static
 int Socket::GetHighestFileDescriptor(
     const Socket& s1, const Socket& s2) {
   return std::max(s1.socket_, s2.socket_);
 }
 
 }  // namespace forwarder