Bug 918970 - display existing thread when sending a sms from contact app

old PR : https://github.com/mozilla-b2g/gaia/pull/16216

I've read [somewhere](https://remysharp.com/2014/11/19/my-five-promise-patterns#throw-over-explicit-reject) (at the end of the paragraph) that I should reject with a real error, not a string. What do you think about that? Do we care about that? 

Related to this blog, does Promise.reject return in Firefox? The author is mentioning that some library does not return when you reject, which means that if you have a resolve later in the code, the promise could end up being fullfilled. For me this behaviour breaks the specs of Promise, but better ask confirmation :-)