Move the js module to a js_sys crate (#512)

* Move the `js` module to a `js_sys` crate

* Update js-sys tests to pass again

* Update binding_to_unimplemented_apis_doesnt_break_everything

Remove its dependency on the `js` module

* Update metadata for js-sys

* Fix the `closures` example

crates/js-sys/tests/all/MapIterator.rs

@@ -0,0 +1,100 @@
+#![allow(non_snake_case)]
+
+use project;
+
+
+#[test]
+fn entries() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(use_extern_macros)]
+
+            extern crate wasm_bindgen;
+            extern crate js_sys;
+            use wasm_bindgen::prelude::*;
+
+            #[wasm_bindgen]
+            pub fn get_entries(this: &js_sys::Map) -> js_sys::MapIterator {
+                this.entries()
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = new Map();
+                const iterator = map.entries();
+                const wasmIterator = wasm.get_entries(map);
+                map.set('foo', 'bar');
+                map.set('bar', 'baz');
+
+                assert.equal(iterator.toString(), wasmIterator.toString());
+            }
+        "#)
+        .test()
+}
+
+#[test]
+fn keys() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(use_extern_macros)]
+
+            extern crate wasm_bindgen;
+            extern crate js_sys;
+            use wasm_bindgen::prelude::*;
+
+            #[wasm_bindgen]
+            pub fn get_keys(this: &js_sys::Map) -> js_sys::MapIterator {
+                this.keys()
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = new Map();
+                const iterator = map.keys();
+                const wasmIterator = wasm.get_keys(map);
+                map.set('foo', 'bar');
+                map.set('bar', 'baz');
+
+                assert.equal(iterator.toString(), wasmIterator.toString());
+            }
+        "#)
+        .test()
+}
+
+#[test]
+fn values() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(use_extern_macros)]
+
+            extern crate wasm_bindgen;
+            extern crate js_sys;
+            use wasm_bindgen::prelude::*;
+
+            #[wasm_bindgen]
+            pub fn get_values(this: &js_sys::Map) -> js_sys::MapIterator {
+                this.values()
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = new Map();
+                const iterator = map.keys();
+                const wasmIterator = wasm.get_values(map);
+                map.set('foo', 'bar');
+                map.set('bar', 'baz');
+
+                assert.equal(iterator.toString(), wasmIterator.toString());
+            }
+        "#)
+        .test()
+}