message: Add STEP_MARK_AT_SECOND_LEVEL_WHILE_LOOP.
diff: @@ -215,6 +215,9 @@ message DebugOptions {
  // Generate a step marker at each iteration of the top level while loop,
  // which is assumed to be a training loop.
  STEP_MARK_AT_TOP_LEVEL_WHILE_LOOP = 1;
  + // Generate a step marker at each iteration of the second level while loops,
  + // which is assumed to be a training or eval loop.
  + STEP_MARK_AT_SECOND_LEVEL_WHILE_LOOP = 3;
  // No step marker generated.
  STEP_MARK_NONE = 2;
  }
  