DNS: Retain stale entries in HostCache and return when requested

net/dns/dns_util.h

Index: net/dns/dns_util.h
diff --git a/net/dns/dns_util.h b/net/dns/dns_util.h
index 1acbd668cdcd7670ed60ba13159ccc5cb79758e7..bd13b7953ad29666e67ed165c152d0244fc4582d 100644
--- a/net/dns/dns_util.h
+++ b/net/dns/dns_util.h
@@ -14,6 +14,8 @@
 
 namespace net {
 
+class AddressList;
+
 // DNSDomainFromDot - convert a domain string to DNS format. From DJB's
 // public domain DNS library.
 //
@@ -40,6 +42,22 @@ base::TimeDelta GetTimeDeltaForConnectionTypeFromFieldTrialOrDefault(
     NetworkChangeNotifier::ConnectionType connection_type);
 #endif  // !defined(OS_NACL)
 
+// Used in histograms; please only insert new entries before MAX.

[Ryan Sleevi, 2016/04/26 02:18:22]

Comment nit: While politeness is a virtue, it leaves ambiguity that it 'might be
ok' to ignore that please.

// Used in histograms. New values should be added at the end, before MAX

[Ryan Sleevi, 2016/04/26 02:18:22]

Comment nit: This doesn't explain the type

// The result of comparing two AddressLists for the set of addresses
// they contain and whether any differences exist.

(Or something?)

[Ryan Sleevi, 2016/04/26 02:18:22]

If they're used in histograms, you should add explicit values. Inserting a value
in between two entries means they would be renumbered and throw off the
histograms.

[Julia Tuttle, 2016/04/27 14:47:04]

Done (all three; the new rietveld UI won't let me reply to individual comments,
just the "thread" attached to the line).

+enum AddressListDeltaType {
+  // a and b contain the same addresses in the same order.

[Ryan Sleevi, 2016/04/26 02:18:22]

nit: "a" and "b" are not defined here (they're an implementation of
FindAddressListDeltaType). Perhaps "Both AddressLists contain the same addresses
in the same order." (and similarly throughout)

[Julia Tuttle, 2016/04/27 14:47:04]

Done.

+  DELTA_IDENTICAL,
+  // a and b contain the same addresses in a different order.
+  DELTA_REORDERED,
+  // a and b have at least one address in common, but not all of them.
+  DELTA_OVERLAP,
+  // a and b have no addresses in common.
+  DELTA_DISJOINT,
+  MAX_DELTA_TYPE

[Ryan Sleevi, 2016/04/26 02:18:22]

naming: Given that you adopted ENUM_PREFIX naming, shouldn't this be
DELTA_MAX_VALUE ?

[Julia Tuttle, 2016/04/27 14:47:04]

I usually make an exception for the max value constant. Is that bad?

+};
+
+AddressListDeltaType FindAddressListDeltaType(const AddressList& a,

[Ryan Sleevi, 2016/04/26 02:18:22]

Document? :)

[Julia Tuttle, 2016/04/27 14:47:04]

Done (the new rietveld UI has no button for this :( ).

+                                              const AddressList& b);
+
 }  // namespace net
 
 #endif  // NET_DNS_DNS_UTIL_H_