message: FixedTypedVector: add const to ElementType() and size()
diff: @@ -320,8 +320,8 @@ class FixedTypedVector : public Object {
  return data_ == FixedTypedVector::EmptyFixedTypedVector().data_;
  }
  - Type ElementType() { return type_; }
  - uint8_t size() { return len_; }
  + Type ElementType() const { return type_; }
  + uint8_t size() const { return len_; }
  private:
  Type type_;
  