Image step slider shows outdated data

[teamdandelion]

If you press "reload" in the TensorBoard UI, the image will reload but the step counter will stay the same, resulting in an inaccurate step count being displayed.

Reproduction:
Run a job that outputs image summaries at a fast rate.
Load the image tab, when a certain step is present (e.g. 1000).
Wait half a minute. Press reload. The image loader will show a new image (e.g. for step 2000). However, the slider will erroneously still display 1000. Dragging the slider to a different step and then back will cause it to correctly display 2000.

[chihuahua]

The audio dashboard interestingly does not exhibit this problem because _currentDatum depends on both _steps and _stepIndex.

tensorboard/tensorboard/plugins/audio/tf_audio_dashboard/tf-audio-loader.html

Line 194 in 693c07c

_computeCurrentDatum(steps, stepIndex) {