[net] Add AsyncDNS.TTL histogram.

net/base/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_BASE_HOST_CACHE_H_
 #define NET_BASE_HOST_CACHE_H_
 
 #include <functional>
 #include <string>
 
@@ skipping 11 matching lines @@
 class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   // Stores the latest address list that was looked up for a hostname.
   struct Entry {
     Entry(int error, const AddressList& addrlist);
     ~Entry();
 
     // The resolve results for this entry.
     int error;
     AddressList addrlist;
+    base::TimeDelta original_ttl;
   };
 
   struct Key {
     Key(const std::string& hostname, AddressFamily address_family,
         HostResolverFlags host_resolver_flags)
         : hostname(hostname),
           address_family(address_family),
           host_resolver_flags(host_resolver_flags) {}
 
     bool operator<(const Key& other) const {
@@ skipping 19 matching lines @@
   explicit HostCache(size_t max_entries);
 
   ~HostCache();
 
   // Returns a pointer to the entry for |key|, which is valid at time
   // |now|. If there is no such entry, returns NULL.
   const Entry* Lookup(const Key& key, base::TimeTicks now);
 
   // Overwrites or creates an entry for |key|.
   // (|error|, |addrlist|) is the value to set, |now| is the current time
-  // |ttl| is the "time to live".
-  void Set(const Key& key,
-           int error,
-           const AddressList& addrlist,
-           base::TimeTicks now,
-           base::TimeDelta ttl);
+  // |ttl| is the "time to live". Returns a pointer to the created entry.
+  Entry* Set(const Key& key,
+             int error,
+             const AddressList& addrlist,
+             base::TimeTicks now,
+             base::TimeDelta ttl);

[cbentzel, 2012/10/11 18:27:30]

Could this just take a base::TimeDelta original_ttl argument, or even a boolean
for "real ttl", that becomes part of Entry()? 

Then you wouldn't need to change ExpiringCache, and this would still return
void.

[szym, 2012/10/11 18:33:21]

The rationale was that changing the signature of Set() will require updating all
host_cache_unittest, and I was being a bit lazy in case we needed to add some
extra fields in the future.

I'll change the signature.

 
   // Empties the cache
   void clear();
 
   // Returns the number of entries in the cache.
   size_t size() const;
 
   // Following are used by net_internals UI.
   size_t max_entries() const;
 
@@ skipping 13 matching lines @@
   // Map from hostname (presumably in lowercase canonicalized format) to
   // a resolved result entry.
   EntryMap entries_;
 
   DISALLOW_COPY_AND_ASSIGN(HostCache);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_HOST_CACHE_H_