[wasm][asm.js] Allow asm.js->wasm codegen in unsafe-eval situations.

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
+
+// 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));
+})();