Make sure prototype chain is preserved for function arguments which are objects

Summary: Fixes: T3206

Test Plan:
- Run this code and change the position of the text:
```
textFont(createFont("monospace"));
var draw = function() {
  background(255, 255, 255);
  fill(255, 0, 0);
  textSize(15);
  textAlign(CENTER, CENTER);
  text("Hi!", 200, 200);
};
```

Reviewers: pamela, john

Subscribers: #cs

Maniphest Tasks: T3206

Differential Revision: http://phabricator.khanacademy.org/D14397