message: [XLA] Allow async copies to be consumed by fusions.
  This was previously to prevent async copies from crossing computation boundaries
  for ops like kCall, but we don't need to do the same for kFusion.
diff: @@ -222,7 +222,8 @@ bool AlternateMemoryBestFitHeap::FindAllocation(
  }
  if (defining_position.instruction->parent() != use.instruction->parent() ||
  - !use.instruction->called_computations().empty()) {
  + (!use.instruction->called_computations().empty() &&
  + use.instruction->opcode() != HloOpcode::kFusion)) {
  VLOG(3) << "Use is in a different computation or calls a computation.";
  // Fail because we do not allow asynchronous copies while in the bodies of
  // other computation.
  