[foozzie] Make Error immutable to prevent changes to stack-trace api

tools/foozzie/v8_mock.js

Index: tools/foozzie/v8_mock.js
diff --git a/tools/foozzie/v8_mock.js b/tools/foozzie/v8_mock.js
index 5217a02666d062a9ad531bac46ec7aa724459afa..4bd3ce54025988eb647ceb60a135453e3f1f92e3 100644
--- a/tools/foozzie/v8_mock.js
+++ b/tools/foozzie/v8_mock.js
@@ -55,6 +55,7 @@ var __PrettyPrint = function __PrettyPrint(msg) { print(msg); };
 Error.prepareStackTrace = function (error, structuredStackTrace) {
   return "";
 };
+Object.freeze(Error)

[Yang, 2017/01/27 08:35:48]

I think using Object.defineProperty to make prepareStackTrace non-writable and
non-configurable should suffice.

 
 // Mock buffer access in float typed arrays because of varying NaN patterns.
 // Note, for now we just use noop forwarding proxies, because they already