[spec] GC objects no-op prevent extensions

document/js-api/index.bs

@@ -1600,7 +1600,7 @@ The internal methods of an [=Exported GC Object=] use the following implementati
 <div algorithm>
   The <dfn>\[[PreventExtensions]] internal method of an Exported GC Object</dfn> <var ignore>O</var> takes no arguments and returns a boolean. It performs the following steps when called:
 
-    1. Return false.
+    1. Return true.
 </div>
 
 <div algorithm>

proposals/gc/MVP-JS.md

@@ -25,7 +25,7 @@ objects supports the following JS operations:
  - `GetPrototypeOf`: returns `null`.
  - `SetPrototypeOf`: returns `false` (and does not set a prototype).
  - `IsExtensible`: returns `false`.
- - `PreventExtensions`: returns `false`.
+ - `PreventExtensions`: returns `true`.
  - `GetOwnProperty`: returns `undefined`.
  - `DefineOwnProperty`: returns `false`.
  - `HasProperty`: returns `false`.

test/js-api/gc/exported-object.tentative.any.js

@@ -113,17 +113,30 @@ test(() => {
 test(() => {
   const struct = functions.makeStruct();
   const array = functions.makeArray();
-  assert_throws_js(TypeError, () => Object.preventExtensions(struct));
-  assert_throws_js(TypeError, () => Object.preventExtensions(array));
+  assert_true(Reflect.preventExtensions(struct));
+  assert_true(Reflect.preventExtensions(array));
+  assert_equals(Object.preventExtensions(struct), struct);
+  assert_equals(Object.preventExtensions(array), array);
 }, "preventExtensions");
 
 test(() => {
   const struct = functions.makeStruct();
   const array = functions.makeArray();
-  assert_throws_js(TypeError, () => Object.seal(struct));
-  assert_throws_js(TypeError, () => Object.seal(array));
+  assert_true(Object.isSealed(struct));
+  assert_true(Object.isSealed(array));
+  assert_equals(Object.seal(struct), struct);
+  assert_equals(Object.seal(array), array);
 }, "sealing");
 
+test(() => {
+  const struct = functions.makeStruct();
+  const array = functions.makeArray();
+  assert_true(Object.isFrozen(struct));
+  assert_true(Object.isFrozen(array));
+  assert_equals(Object.freeze(struct), struct);
+  assert_equals(Object.freeze(array), array);
+}, "freezing");
+
 test(() => {
   const struct = functions.makeStruct();
   const array = functions.makeArray();