[wasm][asm.js] Check if a property key is a PropertyName before assumming it.

test/mjsunit/asm/regress-681707.js

Index: test/mjsunit/asm/regress-681707.js
diff --git a/test/mjsunit/asm/regress-681707.js b/test/mjsunit/asm/regress-681707.js
new file mode 100644
index 0000000000000000000000000000000000000000..9c352eaf409314c2cb35158b477c9a106d6ace36
--- /dev/null
+++ b/test/mjsunit/asm/regress-681707.js
@@ -0,0 +1,18 @@
+// 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
+
+var foo = (function(stdlib) {
+  "use asm";
+  var bar = (stdlib[0]);
+  function foo() { return bar ("lala"); }
+  return foo;
+})(this);
+
+try {
+  nop(foo);
+  foo();
+} catch (e) {
+}