Return const by ref instead of value

net/dns/host_resolver_impl.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/host_resolver_impl.h"
 
 #if defined(OS_WIN)
 #include <Winsock2.h>
 #elif defined(OS_POSIX)
 #include <netdb.h>
@@ skipping 1399 matching lines @@
                                   &addr_list)) {
       // This will destroy the Job.
       CompleteRequests(
           HostCache::Entry(OK, MakeAddressListForRequest(addr_list)),
           base::TimeDelta());
       return true;
     }
     return false;
   }
 
-  const Key key() const {
-    return key_;
-  }
+  const Key& key() const { return key_; }
 
   bool is_queued() const {
     return !handle_.is_null();
   }
 
   bool is_running() const {
     return is_dns_running() || is_proc_running();
   }
 
  private:
@@ skipping 1000 matching lines @@
     dns_client_->SetConfig(dns_config);
     num_dns_failures_ = 0;
     if (dns_client_->GetConfig())
       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", true);
   }
 
   AbortDnsTasks();
 }
 
 }  // namespace net