title: Tensorflow summary event issue
body: <p>I have an issue with the tensorflow summary.
  When i open it within tensorboard, i can see all the graphs, loss, Average precision and all others scalars data.</p>
  <p>As you can see here:
  <a href="https://i.stack.imgur.com/mrUay.png" rel="nofollow noreferrer">Tensorboard</a></p>
  <p>But when i try to extract it to export it into csv, i have nothing.</p>
  <p>I run this code:</p>
  <pre><code>from tensorboard.backend.event_processing.event_accumulator import EventAccumulator
  event_acc = EventAccumulator(r'path2tfeventfolder')
  event_acc.Reload()
  # Show all tags in the log file
  print(event_acc.Tags())
  </code></pre>
  <p>The print is:</p>
  <p><em>{'images': [], 'audio': [], 'histograms': [], 'scalars': [], 'distributions': [], 'tensors': ['eval_side_by_side_0_0', 'eval_side_by_side_1_0', 'eval_side_by_side_2_0', 'eval_side_by_side_3_0', 'eval_side_by_side_4_0', 'eval_side_by_side_5_0' 'PascalBoxes_Precision/mAP@0.5IOU', 'PascalBoxes_PerformanceByCategory/AP@0.5IOU/1', 'PascalBoxes_PerformanceByCategory/AP@0.5IOU/2', 'PascalBoxes_PerformanceByCategory/AP@0.5IOU/3', 'PascalBoxes_PerformanceByCategory/AP@0.5IOU/4', 'PascalBoxes_PerformanceByCategory/AP@0.5IOU/5',
  'Loss/RPNLoss/localization_loss', 'Loss/RPNLoss/objectness_loss', 'Loss/BoxClassifierLoss/localization_loss', 'Loss/BoxClassifierLoss/classification_loss', 'Loss/regularization_loss', 'Loss/total_loss'], 'graph': False, 'meta_graph': False, 'run_metadata': []}</em></p>
  <p><strong>My final goal is to be able to extract the AveragePrecision for each class (6 differents)</strong></p>