Bug 976846 - fix lint
Merge pull request #16790 from alivedise/bugzilla/976846_bubble-tea_followup

Bug 976846 - fix lint, r=me.
Bug 913782 - [Keyboard] Build time default keyboard selection work for
3rd-party keyboard support.
 - make build/settings.js read the default keyboard layout config

 Bug 920431 - [keyboard] keyboard_layout.json should be customizable
   - Refine to make it adopt the config in distribution package
   - Add a separate build step for shared/ folder - shared-makefiles.