[google-analytics] Equivalence of ga(set,...) in analytics.js ?

[SegmentDestinationsBot]

Migrated from #77 by @ferozed

I am porting some ga code to use segment. There are the ga('set', .... ) calls for which I dont see a corresponding version in analytics.

It is not possible to pass in the custom dimensions as properties because they were being set in a different part of the page, and the track/page calls happen elsewhere.

What I am proposing is, we add a Analytics.prototype.set(props) method. The props would be buffered internally. And when users call track or page or identify, the api calls would be merged with those passed in with the set call. This way it would work for all integrations.