[wasm] WebAssembly.Memory.grow() should handle the no instance case

test/mjsunit/regress/wasm/regression-680938.js

Index: test/mjsunit/regress/wasm/regression-680938.js
diff --git a/test/mjsunit/regress/wasm/regression-680938.js b/test/mjsunit/regress/wasm/regression-680938.js
new file mode 100644
index 0000000000000000000000000000000000000000..75c8a457bbd57b08118fd5bce70e9aad2d466f64
--- /dev/null
+++ b/test/mjsunit/regress/wasm/regression-680938.js
@@ -0,0 +1,8 @@
+// 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.
+
+var v17 = {};
+var v32 = {};
+v39 = new WebAssembly.Memory(v32);
+v49 = v39.grow(v17);