message: Make Connection::id() const
  Cr-Commit-Position: refs/heads/master@{#30689}
diff: @@ -86,7 +86,7 @@ class Connection : public CandidatePairInterface,
  ~Connection() override;
  // A unique ID assigned when the connection is created.
  - uint32_t id() { return id_; }
  + uint32_t id() const { return id_; }
  // Implementation of virtual methods in CandidatePairInterface.
  // Returns the description of the local port
  