message: [XLA] Use device sync instead of stream sync for gemm autotuning.
diff: @@ -61,7 +61,9 @@ static StatusOr<absl::optional<se::blas::AlgorithmType>> DoUncachedGemmAutotune(
  se::DeviceMemoryBase reference_result_buffer, se::Stream* stream,
  const se::cuda::RedzoneAllocator& allocator,
  const BufferComparator& comparator, bool crash_on_checking_failure) {
  - TF_RETURN_IF_ERROR(stream->BlockHostUntilDone());
  + if (!stream->parent()->SynchronizeAllActivity()) {
  + return InternalError("Failed to synchronize GPU for autotuning.");
  + }
  VLOG(3) << "Starting autotune of GemmThunk " << gemm->ToString();
  