message: Make debug message more human-readable.
diff: @@ -683,11 +683,10 @@ void Graph::ToGraphDefSubRange(GraphDef* graph_def, int from_node_id) const {
  << " is overflowing the expected number of inputs ("
  << node->num_inputs() << ") for node " << node->DebugString();
  CHECK(inputs[edge->dst_input()] == nullptr)
  - << "Edge " << edge->src()->DebugString() << ":"
  - << edge->dst()->DebugString() << " with dst_input "
  - << edge->dst_input() << " and had pre-existing input edge "
  - << inputs[edge->dst_input()]->src()->DebugString() << ":"
  - << inputs[edge->dst_input()]->dst()->DebugString();
  + << "Edge " << edge->src()->name() << "->" << edge->dst()->name()
  + << " conflicts with pre-existing input edge "
  + << inputs[edge->dst_input()]->src()->name() << "->"
  + << inputs[edge->dst_input()]->dst()->name();
  inputs[edge->dst_input()] = edge;
  }
  