Update from https://crrev.com/315085

net/dns/dns_hosts.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 "net/dns/dns_hosts.h"
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
@@ skipping 113 matching lines @@
 
   const ParseHostsCommaMode comma_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(HostsParser);
 };
 
 void ParseHostsWithCommaMode(const std::string& contents,
                              DnsHosts* dns_hosts,
                              ParseHostsCommaMode comma_mode) {
   CHECK(dns_hosts);
-  DnsHosts& hosts = *dns_hosts;
 
   StringPiece ip_text;
   IPAddressNumber ip;
   AddressFamily family = ADDRESS_FAMILY_IPV4;
   HostsParser parser(contents, comma_mode);
   while (parser.Advance()) {
     if (parser.token_is_ip()) {
       StringPiece new_ip_text = parser.token();
       // Some ad-blocking hosts files contain thousands of entries pointing to
       // the same IP address (usually 127.0.0.1).  Don't bother parsing the IP
       // again if it's the same as the one above it.
       if (new_ip_text != ip_text) {
         IPAddressNumber new_ip;
         if (ParseIPLiteralToNumber(parser.token().as_string(), &new_ip)) {
           ip_text = new_ip_text;
           ip.swap(new_ip);
           family = (ip.size() == 4) ? ADDRESS_FAMILY_IPV4 : ADDRESS_FAMILY_IPV6;
         } else {
           parser.SkipRestOfLine();
         }
       }
     } else {
       DnsHostsKey key(parser.token().as_string(), family);
       base::StringToLowerASCII(&key.first);
-      IPAddressNumber& mapped_ip = hosts[key];
-      if (mapped_ip.empty())
-        mapped_ip = ip;
+      IPAddressNumber* mapped_ip = &(*dns_hosts)[key];
+      if (mapped_ip->empty())
+        *mapped_ip = ip;
       // else ignore this entry (first hit counts)
     }
   }
 }
 
 }  // namespace
 
 void ParseHostsWithCommaModeForTesting(const std::string& contents,
                                        DnsHosts* dns_hosts,
                                        ParseHostsCommaMode comma_mode) {
@@ skipping 34 matching lines @@
   std::string contents;
   if (!base::ReadFileToString(path, &contents))
     return false;
 
   ParseHosts(contents, dns_hosts);
   return true;
 }
 
 }  // namespace net