DNS: Expose stale results through HostResolverImpl.

net/dns/host_resolver_impl.h

Index: net/dns/host_resolver_impl.h
diff --git a/net/dns/host_resolver_impl.h b/net/dns/host_resolver_impl.h
index b3126633fdc8eda660742a2be7a1b088197a0e99..9ab01ca03ea1a6d3ea4a828249d546537a127f4f 100644
--- a/net/dns/host_resolver_impl.h
+++ b/net/dns/host_resolver_impl.h
@@ -138,16 +138,24 @@ class NET_EXPORT HostResolverImpl
               const CompletionCallback& callback,
               RequestHandle* out_req,
               const BoundNetLog& source_net_log) override;
-  int ResolveFromCache(const RequestInfo& info,
-                       AddressList* addresses,
-                       const BoundNetLog& source_net_log) override;
   void ChangeRequestPriority(RequestHandle req,
                              RequestPriority priority) override;
   void CancelRequest(RequestHandle req) override;
+  int ResolveFromCache(const RequestInfo& info,
+                       AddressList* addresses,
+                       const BoundNetLog& source_net_log) override;
   void SetDnsClientEnabled(bool enabled) override;
   HostCache* GetHostCache() override;
   std::unique_ptr<base::Value> GetDnsConfigAsValue() const override;
 
+  // Like |ResolveFromCache()|, but can return a stale result if the
+  // implementation supports it. Fills in |*stale_info| if a response is
+  // returned to indicate how stale (or not) it is.
+  int ResolveStaleFromCache(const RequestInfo& info,
+                            AddressList* addresses,
+                            HostCache::EntryStaleness* stale_info,
+                            const BoundNetLog& source_net_log);
+
   void set_proc_params_for_test(const ProcTaskParams& proc_params) {
     proc_params_ = proc_params;
   }
@@ -181,10 +189,19 @@ class NET_EXPORT HostResolverImpl
   // ERR_NAME_NOT_RESOLVED if either hostname is invalid or IP literal is
   // incompatible, ERR_DNS_CACHE_MISS if entry was not found in cache and
   // HOSTS and is not localhost.
+  //
+  // If |allow_stale| is true, then stale cache entries can be returned.
+  // |stale_info| must be non-null, and will be filled in with details of the
+  // entry's staleness (if an entry is returned).
+  //
+  // If |allow_stale| is false, then stale cache entries will not be returned,
+  // and |stale_info| must be null.
   int ResolveHelper(const Key& key,
                     const RequestInfo& info,
                     const IPAddress* ip_address,
                     AddressList* addresses,
+                    bool allow_stale,
+                    HostCache::EntryStaleness* stale_info,
                     const BoundNetLog& request_net_log);
 
   // Tries to resolve |key| as an IP, returns true and sets |net_error| if
@@ -198,10 +215,19 @@ class NET_EXPORT HostResolverImpl
   // If |key| is not found in cache returns false, otherwise returns
   // true, sets |net_error| to the cached error code and fills |addresses|
   // if it is a positive entry.
+  //
+  // If |allow_stale| is true, then stale cache entries can be returned.
+  // |stale_info| must be non-null, and will be filled in with details of the
+  // entry's staleness (if an entry is returned).
+  //
+  // If |allow_stale| is false, then stale cache entries will not be returned,
+  // and |stale_info| must be null.
   bool ServeFromCache(const Key& key,
                       const RequestInfo& info,
                       int* net_error,
-                      AddressList* addresses);
+                      AddressList* addresses,
+                      bool allow_stale,
+                      HostCache::EntryStaleness* stale_info);
 
   // If we have a DnsClient with a valid DnsConfig, and |key| is found in the
   // HOSTS file, returns true and fills |addresses|. Otherwise returns false.