The reason for this is that it displays multiple actions when clicked on.
The bookmark star has been replaced by the rather blunt plus (+) icon that Google calls Action Box.
If you do, you also may have noticed that the classic star icon, used to add a bookmark to the browser, has been removed at the same time.
If you are running Chrome Canary, and maybe other versions of the web browser as well, you may have noticed the + icon that Google has added to the browser's address bar.
