Fixing some warning due to different signess of char

net/base/dns_util.cc

 // 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.
 
 #include "net/base/dns_util.h"
 
 #include <cstring>
 
 namespace net {
 
@@ skipping 42 matching lines @@
   name[namelen++] = 0;  // This is the root label (of length 0).
 
   *out = std::string(name, namelen);
   return true;
 }
 
 std::string DNSDomainToString(const std::string& domain) {
   std::string ret;
 
   for (unsigned i = 0; i < domain.size() && domain[i]; i += domain[i] + 1) {
-    if (domain[i] < 0 || domain[i] > 63)
+#if CHAR_MIN < 0
+    if (domain[i] < 0)
+      return "";
+#endif
+    if (domain[i] > 63)
       return "";
 
     if (i)
       ret += ".";
 
     if (static_cast<unsigned>(domain[i]) + i + 1 > domain.size())
       return "";
 
     ret += domain.substr(i + 1, domain[i]);
   }
@@ skipping 132 matching lines @@
         break;
     } else {
       return false;
     }
   }
 
   return true;
 }
 
 }  // namespace net