message: Add a clarifying comment; NFC
diff: @@ -118,6 +118,9 @@ class RedzoneAllocator : public ScratchAllocator {
  // isn't necessarily just first.size() - 2 * redzone_size_ because when the
  // user allocation size is not a multiple of 4 bytes, we round up the size of
  // the RHS redzone.
  + //
  + // ScratchAllocators need to free all allocated memory on destruction so we
  + // use `OwningDeviceMemory` here.
  std::vector<std::pair<OwningDeviceMemory, int64>> allocated_buffers_;
  int64 allocated_bytes_excluding_redzones_ = 0;
  