[wasm] Add a magic word and a version number to the binary.

test/mjsunit/wasm/export-table.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");
 
 (function testExportedMain() {
   var kBodySize = 3;
   var kReturnValue = 99;
-  var kNameMainOffset = 4 + 7 + kBodySize + 8 + 1;
+  var kNameMainOffset = kHeaderSize + 4 + 7 + kBodySize + 8 + 1;
 
-  var data = bytes(
+  var data = bytesWithHeader(
     // signatures
     kDeclSignatures, 1,
     0, kAstI32,                  // void -> i32
     // -- main function
     kDeclFunctions,
     1,
     0,                           // decl flags
     0, 0,                        // signature index
     kBodySize, 0,
     // main body
@@ skipping 15 matching lines @@
 
   assertEquals("object", typeof module.exports);
   assertEquals("function", typeof module.exports.main);
 
   assertEquals(kReturnValue, module.exports.main());
 })();
 
 (function testExportedTwice() {
   var kBodySize = 3;
   var kReturnValue = 99;
-  var kNameMainOffset = 4 + 7 + kBodySize + 14 + 1;
+  var kNameMainOffset = kHeaderSize + 4 + 7 + kBodySize + 14 + 1;
   var kNameFooOffset = kNameMainOffset + 5;
 
-  var data = bytes(
+  var data = bytesWithHeader(
     // signatures
     kDeclSignatures, 1,
     0, kAstI32,                  // void -> i32
     // -- main function
     kDeclFunctions,
     1,
     0,                           // decl flags
     0, 0,                        // signature index
     kBodySize, 0,
     // main body
@@ skipping 16 matching lines @@
   var ffi = new Object();
   var module = _WASMEXP_.instantiateModule(data, ffi);
 
   assertEquals("object", typeof module.exports);
   assertEquals("function", typeof module.exports.blah);
   assertEquals("function", typeof module.exports.foo);
 
   assertEquals(kReturnValue, module.exports.blah());
   assertEquals(kReturnValue, module.exports.foo());
 })();