Add jsdoc using node2nix

This is useful when trying to verify changes to Firefox source
documentation.

It feels a bit odd to commit the node2nix-generated output, but on the
other hand, generating it at build time means that it won't be
reproducible.

pkgs/gecko/default.nix

@@ -15,6 +15,7 @@
 , zlib, xorg
 , rust-cbindgen
 , nodejs
+, callPackage
 }:
 
 let
@@ -100,6 +101,9 @@ let
     # NodeJS is used for tooling around JS development.
     nodejs
 
+    # Used for building documentation.
+    (callPackage ../jsdoc {}).jsdoc
+
   ] ++ optionals inNixShell [
     valgrind gdb ccache
     (if stdenv.isAarch64 then null else rr)

pkgs/jsdoc/default.nix

@@ -0,0 +1,17 @@
+# This file has been generated by node2nix 1.6.0. Do not edit!
+
+{pkgs ? import <nixpkgs> {
+    inherit system;
+  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
+
+let
+  nodeEnv = import ./node-env.nix {
+    inherit (pkgs) stdenv python2 utillinux runCommand writeTextFile;
+    inherit nodejs;
+    libtool = if pkgs.stdenv.isDarwin then pkgs.darwin.cctools else null;
+  };
+in
+import ./node-packages.nix {
+  inherit (pkgs) fetchurl fetchgit;
+  inherit nodeEnv;
+}