Support deploying an npm package exporting a formatCode method.

pubspec.yaml

 name: dart_style
-version: 0.2.4
+version: 0.2.5
 author: Dart Team <misc@dartlang.org>
 description: Opinionated, automatic Dart source code formatter.
 homepage: https://github.com/dart-lang/dart_style
 environment:
   sdk: ">=1.8.0 <2.0.0"
 dependencies:
   analyzer: '^0.27.0'
   args: '>=0.12.1 <0.14.0'
   path: '>=1.0.0 <2.0.0'
   source_span: '>=1.1.1 <2.0.0'
+  js: ^0.6.0
+  node_preamble: ^1.0.0
+
 dev_dependencies:
   async: '>=1.0.0 <=2.0.0'
   browser: '>=0.10.0 <0.11.0'
-  grinder: '^0.7.2'
+  grinder: '^0.8.0'
   pub_semver: '^1.2.3'
   scheduled_test: '>=0.12.0 <0.13.0'
   test: '>=0.12.0 <0.13.0'
   yaml: '^2.0.0'
 executables:
   dartfmt: format
   dartformat: format # Allow the old name for compatibility.
 # Tell the bots not to bother building the tests since they don't run in a
 # browser anyway.
 transformers:
 - $dart2js:
     $exclude: 'test/**'