Name collision between properties and global variables

When the following code snippet is compiled with `ADVANCED_OPTIMIZATIONS`

```
function f(node) {
node.foo = null;
}

console.log(f); // to prevent inlining
f(window);
f(window);
```

both `f` and `foo` get renamed to `a`:

```
function a(b){b.a=null}console.log(a);a(window);a(window);
```

causing a JavaScript error at the second `f(window)` call.

Is it possible to robustly prevent such name collisions?

Background: when the D3.js library registers a listener on an event target (such as a window), it [sets the target.__on property](https://github.com/d3/d3-selection/blob/master/src/selection/on.js#L72) potentially overwriting a global symbol that happen to got renamed to the same thing.