src/: Update the remaining include paths of string_split.h to its new location.

net/base/host_mapping_rules.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_mapping_rules.h"
 
 #include "base/logging.h"
-#include "base/string_split.h"
 #include "base/string_util.h"
+#include "base/strings/string_split.h"
 #include "base/strings/string_tokenizer.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/net_util.h"
 
 namespace net {
 
 struct HostMappingRules::MapRule {
   MapRule() : replacement_port(-1) {}
 
   std::string hostname_pattern;
@@ skipping 81 matching lines @@
   map_rules_.clear();
 
   base::StringTokenizer rules(rules_string, ",");
   while (rules.GetNext()) {
     bool ok = AddRuleFromString(rules.token());
     LOG_IF(ERROR, !ok) << "Failed parsing rule: " << rules.token();
   }
 }
 
 }  // namespace net