[wasm] Use the JavaScript WasmModuleBuilder utility in JS tests.

test/mjsunit/wasm/unreachable.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");
 
-var module = (function () {
-  var kFuncWithBody = 9;
-  var kFuncImported = 7;
-  var kBodySize1 = 1;
-  var kMainOffset = kHeaderSize + 6 + kFuncWithBody + kBodySize1 + 1;
+var main = (function () {
+  var builder = new WasmModuleBuilder();
+  builder.addFunction("main", [kAstStmt])
+    .addBody([kExprUnreachable])
+    .exportAs("main");
 
-  var ffi = new Object();
-  ffi.add = (function(a, b) { return a + b | 0; });
-
-  return _WASMEXP_.instantiateModule(bytesWithHeader(
-    // -- signatures
-    kDeclSignatures, 1,
-    0, kAstStmt, // void -> void
-    // -- function #0 (unreachable)
-    kDeclFunctions, 1,
-    kDeclFunctionName | kDeclFunctionExport,
-    0, 0,                      // signature offset
-    kMainOffset, 0, 0, 0,      // name offset
-    kBodySize1, 0,             // body size
-    kExprUnreachable,
-    kDeclEnd,
-    'm', 'a', 'i', 'n', 0      // name
-  ), ffi);
+  return builder.instantiate().exports.main;
 })();
 
-// Check the module exists.
-assertFalse(module === undefined);
-assertFalse(module === null);
-assertFalse(module === 0);
-assertEquals("object", typeof module);
-assertEquals("function", typeof module.main);
-
 var exception = "";
 try {
-    assertEquals(0, module.main());
+    assertEquals(0, main());
 } catch(e) {
     print("correctly caught: " + e);
     exception = e;
 }
 assertEquals("unreachable", exception);