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/Proxy.rs

@@ -0,0 +1,76 @@
+#![allow(non_snake_case)]
+
+use project;
+
+#[test]
+fn new() {
+    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 new_proxy(target: JsValue, handler: js_sys::Object) -> js_sys::Proxy {
+                js_sys::Proxy::new(&target, &handler)
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const target = { a: 100 };
+                const handler = {
+                     get: function(obj, prop) {
+                         return prop in obj ? obj[prop] : 37;
+                     }
+                };
+                const proxy = wasm.new_proxy(target, handler);
+                assert.equal(proxy.a, 100);
+                assert.equal(proxy.b, 37);
+            }
+        "#)
+        .test()
+}
+
+#[test]
+fn revocable() {
+    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 new_revocable_proxy(target: JsValue, handler: js_sys::Object) -> js_sys::Object {
+                js_sys::Proxy::revocable(&target, &handler)
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const target = { a: 100 };
+                const handler = {
+                     get: function(obj, prop) {
+                         return prop in obj ? obj[prop] : 37;
+                     }
+                };
+                const { proxy, revoke } =
+                   wasm.new_revocable_proxy(target, handler);
+                assert.equal(proxy.a, 100);
+                assert.equal(proxy.b, 37);
+                revoke();
+                assert.throws(() => { proxy.a }, TypeError);
+                assert.throws(() => { proxy.b }, TypeError);
+                assert.equal(typeof proxy, "object");
+            }
+        "#)
+        .test()
+}