Bug 1806994 - Define @@toStringTag on the WebAssembly namespace objec…

…t. r=rhunt

Namespace objects have a class string (https://webidl.spec.whatwg.org/#ref-for-dfn-class-string⑨)
so they need to have a @@toStringTag property (https://webidl.spec.whatwg.org/#ref-for-dfn-class-string).

Differential Revision: https://phabricator.services.mozilla.com/D165458

js/src/wasm/WasmJS.cpp

@@ -5334,6 +5334,9 @@ static const JSFunctionSpec WebAssembly_static_methods[] = {
           JSPROP_ENUMERATE),
     JS_FS_END};
 
+static const JSPropertySpec WebAssembly_static_properties[] = {
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly", JSPROP_READONLY), JS_PS_END};
+
 static JSObject* CreateWebAssemblyObject(JSContext* cx, JSProtoKey key) {
   MOZ_RELEASE_ASSERT(HasSupport(cx));
 
@@ -5414,13 +5417,10 @@ static bool WebAssemblyClassFinish(JSContext* cx, HandleObject object,
   return true;
 }
 
-static const ClassSpec WebAssemblyClassSpec = {CreateWebAssemblyObject,
-                                               nullptr,
-                                               WebAssembly_static_methods,
-                                               nullptr,
-                                               nullptr,
-                                               nullptr,
-                                               WebAssemblyClassFinish};
+static const ClassSpec WebAssemblyClassSpec = {
+    CreateWebAssemblyObject,       nullptr, WebAssembly_static_methods,
+    WebAssembly_static_properties, nullptr, nullptr,
+    WebAssemblyClassFinish};
 
 const JSClass js::WasmNamespaceObject::class_ = {
     js_WebAssembly_str, JSCLASS_HAS_CACHED_PROTO(JSProto_WebAssembly),