[Android] Fix gn build for instrumentation tests.

tools/android/common/net.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/common/net.h"
 
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 
 #include "base/strings/stringprintf.h"
 
 namespace tools {
 
 int DisableNagle(int socket) {
   int on = 1;
   return setsockopt(socket, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on));
 }
 
 int DeferAccept(int socket) {
   int on = 1;
   return setsockopt(socket, IPPROTO_TCP, TCP_DEFER_ACCEPT, &on, sizeof(on));
 }
 
 std::string DumpBinary(const char* buffer, size_t length) {
   std::string result = "[";
-  for (int i = 0; i < length; ++i) {
+  for (size_t i = 0; i < length; ++i) {
     base::StringAppendF(&result, "%02x,",
                         static_cast<unsigned char>(buffer[i]));
   }
 
   if (length)
     result.erase(result.length() - 1);
 
   return result + "]";
 }
 
 }  // namespace tools