Vendor dependencies

Let's see how I like this workflow.

vendor/wasm-bindgen/tests/wasm/vendor_prefix.rs

@@ -0,0 +1,48 @@
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+
+#[wasm_bindgen(module = "tests/wasm/vendor_prefix.js")]
+extern "C" {
+    fn import_me(x: &str);
+}
+
+#[wasm_bindgen]
+extern "C" {
+    #[wasm_bindgen(vendor_prefix = webkit)]
+    type MySpecialApi;
+    #[wasm_bindgen(constructor)]
+    fn new() -> MySpecialApi;
+    #[wasm_bindgen(method)]
+    fn foo(this: &MySpecialApi) -> u32;
+
+    #[wasm_bindgen(vendor_prefix = webkit)]
+    type MySpecialApi2;
+    #[wasm_bindgen(constructor)]
+    fn new() -> MySpecialApi2;
+    #[wasm_bindgen(method)]
+    fn foo(this: &MySpecialApi2) -> u32;
+
+    #[wasm_bindgen(vendor_prefix = a, vendor_prefix = b)]
+    type MySpecialApi3;
+    #[wasm_bindgen(constructor)]
+    fn new() -> MySpecialApi3;
+    #[wasm_bindgen(method)]
+    fn foo(this: &MySpecialApi3) -> u32;
+
+    // This API does not exist at all;
+    // test that Rust gets a chance to catch the error (#2437)
+    #[wasm_bindgen(vendor_prefix = a, vendor_prefix = b)]
+    type MyMissingApi;
+    #[wasm_bindgen(constructor, catch)]
+    fn new() -> Result<MyMissingApi, JsValue>;
+}
+
+#[wasm_bindgen_test]
+pub fn polyfill_works() {
+    import_me("foo");
+
+    assert_eq!(MySpecialApi::new().foo(), 123);
+    assert_eq!(MySpecialApi2::new().foo(), 124);
+    assert_eq!(MySpecialApi3::new().foo(), 125);
+    assert!(MyMissingApi::new().is_err());
+}