Ensure that TensorBoard's multiplexer is always loaded, even if there's lots of data.
Ensure that TensorBoard's multiplexer is always loaded, even if there's lots of data.

In current code, if loading data will take a while, requests to the multiplexer will error while data is loading, because some of the EventAccumulators aren't loaded.
Change: 113769073

tensorflow/tensorboard,francoisluus/tensorboard-supervise,agrubb/tensorboard,ioeric/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,shakedel/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,shakedel/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,agrubb/tensorboard,shakedel/tensorboard,ioeric/tensorboard,agrubb/tensorboard,shakedel/tensorboard,agrubb/tensorboard,qiuminxu/tensorboard,ioeric/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,tensorflow/tensorboard,ioeric/tensorboard,qiuminxu/tensorboard,agrubb/tensorboard,agrubb/tensorboard,shakedel/tensorboard,ioeric/tensorboard,francoisluus/tensorboard-supervise,shakedel/tensorboard,qiuminxu/tensorboard,ioeric/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise