Add Certificate Transparency logs auditing

components/certificate_transparency/tree_state_tracker.h

Index: components/certificate_transparency/tree_state_tracker.h
diff --git a/components/certificate_transparency/tree_state_tracker.h b/components/certificate_transparency/tree_state_tracker.h
index 978a909bfddab9105ef80a28bee6abf2c0fb95b4..7523978f34e86b73996ba91ae88d1a70a29b4119 100644
--- a/components/certificate_transparency/tree_state_tracker.h
+++ b/components/certificate_transparency/tree_state_tracker.h
@@ -26,6 +26,7 @@ struct SignedTreeHead;
 }  // namespace net
 
 namespace certificate_transparency {
+class LogDnsClient;
 class SingleTreeTracker;
 
 // This class receives notifications of new Signed Tree Heads (STHs) and
@@ -56,6 +57,12 @@ class TreeStateTracker : public net::CTVerifier::Observer,
   void NewSTHObserved(const net::ct::SignedTreeHead& sth) override;
 
  private:
+  // A Log DNS client for fetching inclusion proof and leaf indices from
+  // DNS front-end of CT logs.
+  // Shared between all SingleTreeTrackers, for rate-limiting across all
+  // trackers. Must be deleted after the tree trackers.
+  std::unique_ptr<LogDnsClient> dns_client_;
+
   // Holds the SingleTreeTracker for each log
   std::map<std::string, std::unique_ptr<SingleTreeTracker>> tree_trackers_;