Cache the checkpoint info requests.
Cache the checkpoint info requests.

We make a call to retrieveCheckpointInfo twice, one to get the info, one for getting the
default tensor. Now the default tensor request is cached, which speeds up load time
because we don't have to make two requests to the server.
Change: 135372133

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