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.
I don't think it's necessary - the XBlock JS runtime will already take care of waiting for the onready event before triggering the XBlock code, so there is no risk of running it too early. It might actually be detrimental in some cases, for example if the XBlock JS is loaded after the initial page load, like in Studio or with jquery-xblock