[wasm][asm.js] Fix and enable several asm.js tests with the new parser.

test/mjsunit/wasm/asm-with-wasm-off.js

 // Copyright 2017 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: --validate-asm --allow-natives-syntax
+// Flags: --validate-asm --allow-natives-syntax --fast-validate-asm
 
 // NOTE: This is in it's own file because it calls %DisallowCodegenFromStrings,
 // which messes with the isolate's state.
 (function testAsmWithWasmOff() {
   %DisallowCodegenFromStrings();
   function Module() {
     'use asm';
     function foo() {
       return 0;
     }
     return {foo: foo};
   }
   Module();
   assertTrue(%IsAsmWasmCode(Module));
 })();