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

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");
 
 var module = (function () {
   var kFuncWithBody = 9;
   var kFuncImported = 7;
   var kBodySize1 = 1;
-  var kMainOffset = 6 + kFuncWithBody + kBodySize1 + 1;
+  var kMainOffset = kHeaderSize + 6 + kFuncWithBody + kBodySize1 + 1;
 
   var ffi = new Object();
   ffi.add = (function(a, b) { return a + b | 0; });
 
-  return _WASMEXP_.instantiateModule(bytes(
+  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,
@@ skipping 10 matching lines @@
 assertEquals("function", typeof module.main);
 
 var exception = "";
 try {
     assertEquals(0, module.main());
 } catch(e) {
     print("correctly caught: " + e);
     exception = e;
 }
 assertEquals("unreachable", exception);