Make HostCache::RestoreFromListValue() take a const reference

net/dns/host_cache.h

Index: net/dns/host_cache.h
diff --git a/net/dns/host_cache.h b/net/dns/host_cache.h
index efc79980c104f2f4440b5c813a452c76c506445e..39c95e4ff4c056424544c6ab63e2661fcdc80772 100644
--- a/net/dns/host_cache.h
+++ b/net/dns/host_cache.h
@@ -171,7 +171,7 @@ class NET_EXPORT HostCache {
   // 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;