Javascript styleguide is outdated compared to internal JS style

[freshp86]

It seems that the Javascript styleguide has not been updated for a while. Specifically see https://google.github.io/styleguide/jsguide.html#file-es6-modules where Javascript modules are banned, whereas they are allowed in Google's internal style.

Could we update the external styleguide? The motivation to update is that we would like to follow it from the Chromium codebase, which is in the process of allowing JS modules usage, see https://groups.google.com/a/chromium.org/d/msg/chromium-dev/-vm0FX3euDc/ueyKDDWQFAAJ.

cc @danbeam