Make HostCache::RestoreFromListValue() take a const reference

net/dns/host_cache.h

 // 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.
 
 #ifndef NET_DNS_HOST_CACHE_H_
 #define NET_DNS_HOST_CACHE_H_
 
 #include <stddef.h>
 
 #include <functional>
@@ skipping 153 matching lines @@
   // Clears hosts matching |host_filter| from the cache.
   void ClearForHosts(
       const base::Callback<bool(const std::string&)>& host_filter);
 
   // Returns the contents of the cache represented as a base::ListValue for
   // serialization.
   std::unique_ptr<base::ListValue> GetAsListValue(bool include_staleness) const;
   // Takes a base::ListValue representing cache entries and stores them in the
   // cache, skipping any that already have entries. Returns true on success,
   // false on failure.
-  bool RestoreFromListValue(base::ListValue& old_cache);
+  bool RestoreFromListValue(const base::ListValue& old_cache);
 
   // Returns the number of entries in the cache.
   size_t size() const;
 
   // Following are used by net_internals UI.
   size_t max_entries() const;
   int network_changes() const { return network_changes_; }
   const EntryMap& entries() const { return entries_; }
 
   // Creates a default cache.
@@ skipping 35 matching lines @@
   EvictionCallback eviction_callback_;
 
   THREAD_CHECKER(thread_checker_);
 
   DISALLOW_COPY_AND_ASSIGN(HostCache);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_CACHE_H_