message: [CancellationManager] Initialize `State::first_child` to nullptr.
diff: @@ -150,7 +150,7 @@ class CancellationManager {
  // If this CancellationManager has any children, this member points to the
  // head of a doubly-linked list of its children.
  - CancellationManager* first_child; // Not owned.
  + CancellationManager* first_child = nullptr; // Not owned.
  };
  bool RegisterChild(CancellationManager* child);
  