message: Add comment that explicitly states that InitTableIterator is Thread-unsafe.
diff: @@ -92,6 +92,8 @@ class InitializableLookupTable : public LookupInterface {
  //
  // Then the iterator is exhausted, valid returns false and status returns
  // Status::OutOfRange.
  + //
  + // This class is Thread-unsafe.
  class InitTableIterator {
  public:
  InitTableIterator() {}
  