Vendor dependencies

Let's see how I like this workflow.

vendor/wasm-bindgen/tests/wasm/duplicate_deps.js

@@ -0,0 +1,17 @@
+const assert = require('assert');
+
+let next = null;
+
+exports.assert_next_undefined = function() {
+  next = undefined;
+};
+
+exports.assert_next_ten = function() {
+  next = 10;
+};
+
+exports.foo = function(a) {
+  console.log(a, next);
+  assert.strictEqual(a, next);
+  next = null;
+};