message: Move the JSON mappig generation to allow for VLOG output even with OOM
  Summary: Make it so that the mapping is done indepenedent of the OOM
  Test Plan: None
  Reviewers: jakeh, georgep
diff: @@ -373,6 +373,10 @@ StatusOr<std::unique_ptr<Executable>> PoplarCompiler::RunBackend(
  graph.outputVertexGraph(stream, progs);
  }
  + // Generate this JSON early so that the VLOG trace can contain the output
  + // whether the engine compilation completes or not
  + std::string map_json = GetTensorMappingJson(graph, resources.tensor_maps);
  +
  is_remap_graph = AreAllOutputsParameters(
  entry->root_instruction(), visitor.GetNonStandardParameterLayout(),
  remaped_output);
  @@ -416,8 +420,6 @@ StatusOr<std::unique_ptr<Executable>> PoplarCompiler::RunBackend(
  }
  }
  - std::string map_json = GetTensorMappingJson(graph, resources.tensor_maps);
  -
  uint64 duration = tensorflow::Env::Default()->NowMicros() - start_micros;
  poplarExecutor->AddCompileEndEventRecord(module->name(), stream.str(),
  