Add stylelint dependency

This also adds CC-BY-4.0 to the list of accepted licenses.

DISABLE_THIRD_PARTY_CHECK=update dependencies

Bug: chromium:1083142
Change-Id: I8612de2fba52dae32eeb71af79d5aacfde52142b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2220097
Reviewed-by: Paul Lewis <aerotwist@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
diff --git a/node_modules/array-union/index.js b/node_modules/array-union/index.js
new file mode 100644
index 0000000..7f85d3d
--- /dev/null
+++ b/node_modules/array-union/index.js
@@ -0,0 +1,5 @@
+'use strict';
+
+module.exports = (...arguments_) => {
+	return [...new Set([].concat(...arguments_))];
+};