Cronet: Use stale DNS cache entries experimentally.

net/dns/host_resolver.h

Index: net/dns/host_resolver.h
diff --git a/net/dns/host_resolver.h b/net/dns/host_resolver.h
index 5c371e43ad533e66ed0f366c36f5f17bb73e1bf7..b1f62e0a772bfeb7c439ef3ec4d54ad0ee43d8f1 100644
--- a/net/dns/host_resolver.h
+++ b/net/dns/host_resolver.h
@@ -28,6 +28,7 @@ namespace net {
 
 class AddressList;
 class BoundNetLog;
+class HostResolverImpl;
 class HostResolverProc;
 class NetLog;
 
@@ -192,9 +193,18 @@ class NET_EXPORT HostResolver {
   static std::unique_ptr<HostResolver> CreateSystemResolver(
       const Options& options,
       NetLog* net_log);
+  // Same, but explicitly returns the HostResolverImpl. Only used by
+  // StaleHostResolver in cronet.
+  static std::unique_ptr<HostResolverImpl> CreateSystemResolverImpl(

[xunjieli, 2016/07/25 17:18:15]

Is this preferred over doing a runtime cast of HostResolver to HostResolverImpl?

[Julia Tuttle, 2016/07/25 19:29:16]

They're both ugly; I think this is slightly less ugly, because it means someone
who wants to change what CreateSystemResolver returns will have to think about
it instead of just breaking things.

[xunjieli, 2016/07/25 21:09:14]

Acknowledged.

+      const Options& options,
+      NetLog* net_log);
 
   // As above, but uses default parameters.
   static std::unique_ptr<HostResolver> CreateDefaultResolver(NetLog* net_log);
+  // Same, but explicitly returns the HostResolverImpl. Only used by
+  // StaleHostResolver in cronet.
+  static std::unique_ptr<HostResolverImpl> CreateDefaultResolverImpl(
+      NetLog* net_log);
 
  protected:
   HostResolver();