Google Drive XBlock - Fake PR for review purposes, do not merge!

@martynjames Created this PR for the review. 

Btw for the future, it's easier to create this when the first commit is empty. Also, if we want to review a series of PRs at once instead of individual PRs, it would be easier to merge the individual PRs in a branch which isn't master, and then create a PR from that branch into master when it's ready -- this way we don't need "fake" PRs at all, they represent the actual review workflow.
If this is an endpoint to allow for clients to fire events that get into the analytics pipeline, it might be advisable to have a more generic endpoint here that is not tied to the specific event. For example, what would you do if you wanted to add another event type? In this pattern you'd have to make another json_handler.

how about a generic:

def publish_event(self, type, data, ...)

Not a must have, just a suggestion.