web_testing.bzl: fix miscellaneous lint errors (#1673)
web_testing.bzl: fix miscellaneous lint errors (#1673)

Summary:

  - Change “Arguments” to “Args”
  - Document the `name` parameter
  - Reformat with `buildifier`

Recommend reviewing with `-w`.

Test Plan:
None.

wchargin-branch: buildify-webtesting
tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard