Check a Web Extension project for basic lint problems.

**Job Variables**

.. zuul:jobvar:: source_dir
   :default: src

   Folder where the uncompressed extension files are located (if you use a tool
   –such as Webpack– to build your extension, this folder should have the
   compiled files which you would ZIP and upload to the extensions store. If
   this is a relative path, it is computed as if you were in the directory
   ``{{ zuul.project.src_dir }}``.

.. zuul:jobvar:: extra_lint_flags

   Optional: string with flags that will be passed to the web-ext lint command,
   if specified.