At this time Mendeley does not have a "add on" in the Google Store to work with Google Docs.
If you are citing sources in your Mendeley library and are using Google Docs or Google Slides and need to create an informal bibliography list
you can by going to Mendeley and selecting your citations then click near the bottom of the Mendeley page on "Copy as" and a list of selections will appear.
Click on "formatted citation". When you do this a message will appear that it has been saved to the clipboard. Then open Google Docs or Google Slides and paste on to the area of the doc or slide you would like to citations.