Google quietly updated the free Google Drive app to version 3.4.0 yesterday, improving the iOS version with some features that should make Google's cloud solution more competitive with the likes of iCloud drive and Dropbox.
The biggest addition for iPhone and iPad users who have upgraded to iOS 8 is that they'll now be able to add documents from other applications to their Google Drive storage. This is done through an app's share sheet, specifically when you choose to "Open in Google Drive" (see image at top of this post).
As a test, I was able to send an image from Waterlogue, a letter written in Pages, and output from several other recently-updated apps to Google Drive. Older apps, and those that haven't been updated in some time, may not be able to use this capability.
Google also announced that iOS Google Drive users will be able to access and share maps that were custom-made through the My Maps feature. Those custom maps need to be created using the web version of Drive, but are then able to be opened in Safari or Chrome and shared with others.