LogDnsClient now returns some errors synchronously

components/certificate_transparency/log_dns_client.h

Index: components/certificate_transparency/log_dns_client.h
diff --git a/components/certificate_transparency/log_dns_client.h b/components/certificate_transparency/log_dns_client.h
index 0109ee28007678f24a0669448843a372a71825c7..47fd5d3855cc74b60db7ca0970258c421e50dfb1 100644
--- a/components/certificate_transparency/log_dns_client.h
+++ b/components/certificate_transparency/log_dns_client.h
@@ -6,22 +6,19 @@
 #define COMPONENTS_CERTIFICATE_TRANSPARENCY_LOG_DNS_CLIENT_H_
 
 #include <stdint.h>
 
 #include <list>
-#include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 #include "net/base/network_change_notifier.h"
 #include "net/log/net_log.h"
 
 namespace net {
 class DnsClient;
-class DnsResponse;
-class DnsTransaction;
 namespace ct {
 struct MerkleAuditProof;
 }  // namespace ct
 }  // namespace net
 
@@ -69,14 +66,14 @@ class LogDnsClient : public net::NetworkChangeNotifier::DNSObserver {
   // The |leaf_hash| is the SHA-256 Merkle leaf hash (see RFC6962, section 2.1).
   // The size of the CT log tree must be provided in |tree_size|.
   // The log is identified by |domain_for_log|, which is the DNS name used as a
   // suffix for all queries.
   // The |callback| is invoked when the query is complete, or an error occurs.

[Eran Messeri, 2016/09/28 13:44:08]

Document the return value - that on successful submission ERR_IO_PENDING  will
be returned, another error code to indicate throttling (and everything else is a
hard-fail).

[Rob Percival, 2016/09/28 16:19:14]

Done.

-  void QueryAuditProof(const std::string& domain_for_log,
-                       base::StringPiece leaf_hash,
-                       uint64_t tree_size,
-                       const AuditProofCallback& callback);
+  int QueryAuditProof(base::StringPiece domain_for_log,

[Eran Messeri, 2016/09/28 13:44:08]

Question to rsleevi: Why not use net::Error here?

+                      base::StringPiece leaf_hash,
+                      uint64_t tree_size,
+                      const AuditProofCallback& callback);
 
  private:
   // An audit proof query that is in progress.
   class AuditProofQuery;
 
@@ -100,10 +97,12 @@ class LogDnsClient : public net::NetworkChangeNotifier::DNSObserver {
   // Used to perform DNS queries.
   std::unique_ptr<net::DnsClient> dns_client_;
   // Passed to the DNS client for logging.
   net::BoundNetLog net_log_;
   // Audit proof queries that haven't completed yet.
+  // Expected to typically be a FIFO queue of queries, so a std::list should be
+  // efficient.

[Eran Messeri, 2016/09/28 13:44:08]

Be more explicit in the comment:
// A FIFO queue of queries. Since entries will always be appended to the
// end of the queue and lookups will yield entries at the beginning,
// std::list is the efficient choice.

[Rob Percival, 2016/09/28 16:19:14]

Done.

   std::list<std::unique_ptr<AuditProofQuery>> audit_proof_queries_;
   // The maximum number of queries that can be in flight at one time.
   size_t max_concurrent_queries_;
   // Creates weak_ptrs to this, for callback purposes.
   base::WeakPtrFactory<LogDnsClient> weak_ptr_factory_;