[wasm] Require wasm explicit asm instantiation to be of a function.

test/mjsunit/regress/regress-wasm-crbug-620649.js

Index: test/mjsunit/regress/regress-wasm-crbug-620649.js
diff --git a/test/mjsunit/regress/regress-wasm-crbug-620649.js b/test/mjsunit/regress/regress-wasm-crbug-620649.js
new file mode 100644
index 0000000000000000000000000000000000000000..f9355d88874f95c765364c161ddb33c0815dc7ee
--- /dev/null
+++ b/test/mjsunit/regress/regress-wasm-crbug-620649.js
@@ -0,0 +1,10 @@
+// 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
+
+__v_1 = "var outer = 0; function test() {'use strict'; outer = 1; } test();";
+assertThrows(function() {
+  Wasm.instantiateModuleFromAsm(__v_1);
+});