Bug 1024507: Measure use of Twitter and Facebook

The ga calls should show up in the developer console. I grabbed your fork's latest branch of the code, but I still see `ga(set, dimension5, Yes)` and `ga(set, dimension6, Yes)` coming **after** `ga(send, pageview, )` so I'm not sure the pageview will be recorded with the dimension set.

We should [send the dimension data](https://developers.google.com/analytics/devguides/collection/analyticsjs/custom-dims-mets#sendingdata) **before** or **during** the `ga(send, pageview)`.

![mdn_research_dimensions_after_pageview](https://cloud.githubusercontent.com/assets/71928/4320930/a5793a8c-3f3b-11e4-95b9-2959f3011bf6.png)