UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36

Steps to reproduce the problem:
1. Open devtool console

2. Evaluate this snipped to bleach out few methods of Object.prototype:

```
Object.defineProperty(Object.prototype, '__defineGetter__', {
    value: null
});
Object.defineProperty(Object.prototype, '__defineSetter__', {
    value: null
});
```

3. try to inspect any global variable, or define new one, e.g.:

```
f = 1
```

What is the expected behavior?
`f` should be define.

What went wrong?
Uncaught TypeError: this.__defineGetter__ is not a function

Did this work before? N/A 

Chrome version: 48.0.2564.116  Channel: stable
OS Version: OS X 10.10.5
Flash Version: Shockwave Flash 21.0 r0

Safari DevTool suffers from the same issue, FF works fine.

Proposal: rely on `SafeBuiltins` for any operation.