[net] Add AsyncDNS.TTL histogram.

net/base/host_cache.h

Index: net/base/host_cache.h
diff --git a/net/base/host_cache.h b/net/base/host_cache.h
index 7aff49c1ba16dc85cd145c9298ed2314e3ad953e..c700c9cd9c9351b915da2815cab0aac654c3f776 100644
--- a/net/base/host_cache.h
+++ b/net/base/host_cache.h
@@ -29,6 +29,7 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
     // The resolve results for this entry.
     int error;
     AddressList addrlist;
+    base::TimeDelta original_ttl;
   };
 
   struct Key {
@@ -68,12 +69,12 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
 
   // 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();