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.
Are these in the documentation because there are cases where the current defaults for width/height would not be good? If that's the case it might be worth making them XBlock fields the user can set?