[wasm] Freeze exports object

test/mjsunit/wasm/instantiate-module-basic.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-wasm
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
 let kReturnValue = 117;
 
 let buffer = (() => {
   let builder = new WasmModuleBuilder();
   builder.addMemory(1, 1, true);
   builder.addFunction("main", kSig_i_v)
     .addBody([kExprI8Const, kReturnValue])
     .exportFunc();
 
   return builder.toBuffer();
 })()
 
 function CheckInstance(instance) {
   assertFalse(instance === undefined);
   assertFalse(instance === null);
   assertFalse(instance === 0);
   assertEquals("object", typeof instance);
 
+  // Check the exports object is frozen.
+  assertFalse(Object.isExtensible(instance.exports));
+  assertTrue(Object.isFrozen(instance.exports));
+
   // Check the memory is an ArrayBuffer.
   var mem = instance.exports.memory;
   assertFalse(mem === undefined);
   assertFalse(mem === null);
   assertFalse(mem === 0);
   assertEquals("object", typeof mem);
   assertTrue(mem instanceof WebAssembly.Memory);
   var buf = mem.buffer;
   assertTrue(buf instanceof ArrayBuffer);
   assertEquals(65536, buf.byteLength);
@@ skipping 175 matching lines @@
   assertEquals(1, i1.exports.f());
   assertEquals(1000, i2.exports.f());
 })();
 
 (function MustBeMemory() {
   print("MustBeMemory...");
   var memory = new ArrayBuffer(65536);
   var module = new WebAssembly.Module(buffer);
   assertThrows(() => new WebAssembly.Instance(module, null, memory), TypeError);
 })();