Experiment library (cxApi) missing methods even when loaded.

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Name of affected component: Web Tracking (analytics.js)

Issue summary:

In certain conditions (which I have not fully isolated yet) the cxApi library 
loads, but only has two methods/attributes - setCookiePath and chooseVariation 
- available.

This runs counter to what I understood from the documentation that all the 
functions (getChosenVariation, setChosenVariation, etc) would be available on 
cxApi provided the library has loaded.

URL of the page exhibiting the issue: https://vessel.com

Steps to reproduce issue:

Unfortunately, I have not determined repro steps yet. We identified this issue 
from error tracking software deployed on our site. Certain users experienced an 
uncaught error when our code attempted to call cxApi.getChosenVariation(). 
Another line of JS just above this one called cxApi.chooseVariation() with no 
failure, and the cxApi global was available and defined on the page.

Expected output:

cxApi should in theory always have all its methods present once it is loaded.

Actual results:

Sometimes cxApi is defined, but only has two methods (chooseVariation and 
setCookiePath).

Notes:

After this happened on our site, I added a null check for the 
getChosenVariation function, and then sent a debugging beacon with the keys of 
the cxApi object to our backend in the event that that getChosenVariation 
function was undefined. From this, I determined that sometimes the object only 
has the two keys "chooseVariation" and "setCookiePath".

Watered down example GIST of the code which errored: 
https://gist.github.com/alexhancock/ae8f9fd98923d9a27d03

A screenshot of a JS tracktrace we got in a bug report from one of our users: 
https://pbs.twimg.com/media/CG6gUbKUYAEBYVI.png

Original issue reported on code.google.com by alexhanc...@gmail.com on 10 Jun 2015 at 10:16