ES6 object property fields

From `es6.js`:

```
def("Property")
.field("key", or(def("Literal"), def("Identifier"), def("Expression")))
.field("value", or(def("Expression"), def("Pattern")))
.field("method", Boolean, defaults["false"])
.field("shorthand", Boolean, defaults["false"])
.field("computed", Boolean, defaults["false"]);
```

How do I set the `method`, `shorthand`, and `computed` fields of a property?
I might be wrong, but shouldn't `build` be called with these properties?

Read the Property definition in es6.js, then trace the build entry point to see how method, shorthand, and computed are handled. Done means establishing whether build accepts these fields and recording or implementing the expected behavior with a corresponding verification.

Written by the indexing model from the issue text.