message: Reduce overhead in Executor critical section.
  This change changes two incidences of `InlinedVector<TaggedNode>::push_back()` (of a newly constructed TaggedNode) into `InlinedVector<TaggedNode>::emplace_back()`. Since one of these instances happens in `ExecutorState::FrameState::ActivateNodes()`, which is called when the FrameState mutex is held, the serial performance improvement should compound with reduced contention on that mutex.
diff: @@ -2419,8 +2419,7 @@ void ExecutorState::DeleteFrame(FrameState* frame, TaggedNodeSeq* ready) {
  }
  if (dst_ready) {
  if (IsControlTrigger(dst_node)) dst_dead = false;
  - ready->push_back(
  - TaggedNode(dst_node, parent_frame, parent_iter, dst_dead));
  + ready->emplace_back(dst_node, parent_frame, parent_iter, dst_dead);
  parent_iter_state->outstanding_ops++;
  }
  }
  @@ -2544,7 +2543,7 @@ void ExecutorState::FrameState::ActivateNodes(const NodeItem* item,
  // Add dst to the ready queue if it's ready
  if (dst_ready) {
  if (dst_item->is_control_trigger) dst_dead = false;
  - ready->push_back(TaggedNode(dst_item->node, this, iter, dst_dead));
  + ready->emplace_back(dst_item->node, this, iter, dst_dead);
  iter_state->outstanding_ops++;
  }
  }
  