Add `toExportBuilder` to `ReferenceBuilder`

[zoechi]

https://gitter.im/dart-lang/TALK-general/archives/2016/12/01

I could see a Reference.toExportBuilder, would that help?

from

Günter Zöchbauer @zoechi Dec 01 18:56
@matanlurey code_builder question.
Do you know a way to get the import path back from a reference('name', 'path').
I try to create an export and I thing it would be nice if I could use the reference I already have.

Matan Lurey @matanlurey Dec 01 19:06
@zoechi No that is not possible. I don't expose anything you used to build - just complicates the API.

Günter Zöchbauer @zoechi Dec 01 19:08
@matanlurey didn't mean anyting, but it seemes reasonable to use a reference to build an export.

Matan Lurey @matanlurey Dec 01 19:09
I could see a Reference.toExportBuilder, would that help?

[zoechi]

great, thanks :-)