Needs toJSON defined

[toddreifsteck]

Today, Chrome does not return the collection when toJSON is called. This is correct per the spec, but I believe is unexpected. I believe the toJSON should include the collection.

[igrigorik]

Re, spec. I think we just need to add https://github.com/w3c/resource-timing/pull/114/files?

[toddreifsteck]

Maybe.. but today, Chrome has a bug where the inner collection isn't serialized although everything else is. I'm not sure if that is due to incorrect WebIDL or just a bug in Chrome.

[igrigorik]

@spanicker do we have a crbug for this? If not, we should probably file one.

[tdresser]

I think this is a dupe of #37.