[net] Add AsyncDNS.TTL histogram.

net/base/host_cache.cc

Index: net/base/host_cache.cc
diff --git a/net/base/host_cache.cc b/net/base/host_cache.cc
index f94b6869d76bf4e0b1f76f6117ded61774c93c9f..ec35f78f41805856536762885b5b50d3de9023c5 100644
--- a/net/base/host_cache.cc
+++ b/net/base/host_cache.cc
@@ -37,16 +37,16 @@ const HostCache::Entry* HostCache::Lookup(const Key& key,
   return entries_.Get(key, now);
 }
 
-void HostCache::Set(const Key& key,
-                    int error,
-                    const AddressList& addrlist,
-                    base::TimeTicks now,
-                    base::TimeDelta ttl) {
+HostCache::Entry* HostCache::Set(const Key& key,
+                                 int error,
+                                 const AddressList& addrlist,
+                                 base::TimeTicks now,
+                                 base::TimeDelta ttl) {
   DCHECK(CalledOnValidThread());
   if (caching_is_disabled())
-    return;
+    return NULL;
 
-  entries_.Put(key, Entry(error, addrlist), now, now + ttl);
+  return entries_.Put(key, Entry(error, addrlist), now, now + ttl);
 }
 
 void HostCache::clear() {