Google Drive associates default apps like Google Docs, Google Drawings etc for opening, viewing or editing stored files. However, external apps and Chrome extensions too can be added by connecting them. This can be useful when say there are stored photos which need to be edited directly online with the help of an app/extension.
Here is how :
Using Google Chrome, open Google Drive and access Settings.
Manage Apps section will list the default apps associated with various files types. To add external apps that need to be associated, click Connect more apps.
This will launch Web Store. Choose the required extensions/apps that are to be added. Those that are already connected to Google Drive will have a green tick on top.
The selected app will now be connected.
It will now also be listed along with other apps. At any time, these can be removed or be changed from being used as a default.