feat(js) Implement the Date.UTC binding.

src/js.rs

@@ -516,6 +516,15 @@ extern {
     #[wasm_bindgen(method, js_name = toUTCString)]
     pub fn to_utc_string(this: &Date) -> JsString;
 
+    /// The `Date.UTC()` method accepts the same parameters as the
+    /// longest form of the constructor, and returns the number of
+    /// milliseconds in a `Date` object since January 1, 1970,
+    /// 00:00:00, universal time.
+    ///
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/UTC
+    #[wasm_bindgen(static_method_of = Date, js_name = UTC)]
+    pub fn utc(year: Number, month: Number) -> Number;
+
     /// The valueOf() method  returns the primitive value of
     /// a Date object.
     ///

tests/all/js_globals/Date.rs

@@ -304,6 +304,32 @@ fn to_utc_string() {
         .test()
 }
 
+#[test]
+fn utc() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro, wasm_custom_section)]
+
+            extern crate wasm_bindgen;
+            use wasm_bindgen::prelude::*;
+            use wasm_bindgen::js::{Date, Number};
+
+            #[wasm_bindgen]
+            pub fn utc() -> Number {
+                Date::utc(Number::new(JsValue::from(2018)), Number::new(JsValue::from(6)))
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                assert.equal(wasm.utc(), 1530403200000);
+            }
+        "#)
+        .test()
+}
+
 #[test]
 fn value_of() {
     project()