message: Extend the memory optimizations to also support accumulate_n ops
diff: @@ -490,12 +490,12 @@ void RecomputationRewritingPass(RewriterConfig::MemOptType optimization_level,
  }
  bool SchedulingPass(Cluster* cluster, GrapplerItem* item) {
  - // Look for AddN nodes and record input names.
  + // Look for AddN nodes (and equivalent) and record input names.
  GraphView view(&item->graph);
  std::unordered_map<string, std::unordered_set<NodeDef*>> addn_list;
  for (NodeDef& node : *item->graph.mutable_node()) {
  - if (!IsAddN(node)) {
  + if (!IsAddN(node) && node.op() != "AccumulateNV2") {
  continue;
  }
  // There is nothing to gain by optimizing nodes with 2 or fewer inputs.
  