message: Added environment flags to enable output of graphs in pbtxt and dot format.
diff: #include "tensorflow/core/platform/default/logging.h"
  #include "tensorflow/core/platform/protobuf.h"
  +#include "ngraph_log.h"
  +
  using namespace std;
  namespace ngraph_bridge {
  const char* const DEVICE_NGRAPH = "NGRAPH";
  @@ -36,6 +38,12 @@ const char* const DEVICE_NGRAPH = "NGRAPH";
  // GraphToPbTextFile
  //-----------------------------------------------------------------------------
  void GraphToPbTextFile(tf::Graph* graph, const string& filename) {
  + if (std::getenv("NGRAPH_GENERATE_GRAPHS_PBTXT") == nullptr) {
  + NGRAPH_VLOG(3) << "NGRAPH_GENERATE_GRAPHS_PBTXT not set. Not "
  + "generating output graph";
  + return;
  + }
  +
  tf::GraphDef g_def;
  graph->ToGraphDef(&g_def);
  @@ -50,6 +58,12 @@ void GraphToPbTextFile(tf::Graph* graph, const string& filename) {
  //-----------------------------------------------------------------------------
  void GraphToDotFile(tf::Graph* graph, const std::string& filename,
  const std::string& title, bool annotate_device) {
  + if (std::getenv("NGRAPH_GENERATE_GRAPHS_DOT") == nullptr) {
  + NGRAPH_VLOG(3) << "NGRAPH_GENERATE_GRAPHS_DOT not set. Not "
  + "generating output graphviz graph";
  + return;
  + }
  +
  std::string dot = GraphToDot(graph, title, annotate_device);
  std::ofstream ostrm_out(filename, std::ios_base::trunc);
  ostrm_out << dot;
  