webidl: All interfaces implicitly extend Object

This information is embedded within the algorithm for constructing interfaces
and their prototypes in the section for ECMAScript glue in the WebIDL spec...

This really *should* make the `wasm_bindgen_backend::ast::ImportType::extends`
member from a `Vec<Ident>` into a `Vec<syn::Path>` so that we could use
`js_sys::Object` in the extends field, but that is a huge pain because then the
`ImportedTypes` trait needs to be changed, and all of its implementers, etc...

crates/webidl-tests/array.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/array.rs"));

crates/webidl-tests/array_buffer.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/array_buffer.rs"));

crates/webidl-tests/callbacks.rs

@@ -1,5 +1,5 @@
 use wasm_bindgen_test::*;
-use js_sys::Function;
+use js_sys::{Function, Object};
 
 include!(concat!(env!("OUT_DIR"), "/callbacks.rs"));
 

crates/webidl-tests/consts.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/consts.rs"));

crates/webidl-tests/enums.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/enums.rs"));

crates/webidl-tests/global.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/global.rs"));

crates/webidl-tests/simple.rs

@@ -1,9 +1,17 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 use wasm_bindgen::prelude::*;
 use wasm_bindgen::JsCast;
 
 include!(concat!(env!("OUT_DIR"), "/simple.rs"));
 
+#[wasm_bindgen_test]
+fn interfaces_inherit_from_object() {
+    let m = Method::new(42.0).unwrap();
+    assert!(m.is_instance_of::<Object>());
+    let _: &Object = m.as_ref();
+}
+
 #[wasm_bindgen_test]
 fn method() {
     let pi = Method::new(3.14159).unwrap();

crates/webidl-tests/throws.rs

@@ -1,3 +1,4 @@
+use js_sys::Object;
 use wasm_bindgen_test::*;
 
 include!(concat!(env!("OUT_DIR"), "/throws.rs"));