closure_js_deps skips es6 modules

closure_js_deps uses depswriter.py, which has no support for es6 modules.
I was looking at adding es6 support to depswriter then I saw that closure compiler already has a DepsGenerator class with support for es6. closure_js_deps should use this to generate deps.js

Start at closure_js_deps and depswriter.py to understand how deps.js is currently generated. Read the Closure Compiler DepsGenerator support for ES6 modules, then verify that closure_js_deps uses it and that generated deps.js includes ES6 module dependencies.

Written by the indexing model from the issue text.