[wasm] Use the right context in the wasm-to-js wrapper.

test/mjsunit/wasm/wasm-realms.js

+// Copyright 2016 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");
+
+(function testImportsUseTheInstantiateRealm() {
+  print("testImportsUseTheInstantiateRealm");
+  Realm.create();
+
+  Object.prototype.valueOf = function() { return 1; };
+
+  var builder = new WasmModuleBuilder();
+
+  var sig_index = builder.addType(kSig_i);
+  builder.addImport("func", sig_index);
+  builder.addFunction("main", sig_index)
+    .addBody([
+      kExprCallImport, kArity0, 0  // --
+    ])        // --
+    .exportFunc();
+
+  var func = function() {return {};};
+  var main = builder.instantiate({func: func}).exports.main;
+  assertEquals(1, main());
+  Realm.eval(1, "Object.prototype.valueOf = function() { return 2; };");
+  assertEquals(1, main());
+  assertEquals(1, Realm.eval(1, "x => { return x(); };")(main));
+  Object.prototype.valueOf = function() { return 3; };
+  assertEquals(3, main());
+  assertEquals(3, Realm.eval(1, "x => { return x(); };")(main));
+})();