EVOLUTION OF GMAIL CHAT
Official Gmail Blog: Evolution of Gmail chat
Google on its way to improve Gmail, collect user feedback about the feature and use it to know the performance of their features added to their app.
earlier Google added chat mole or chat pop up window to Gmail, now trying out with ideas of "chat within threads"
you will be able to chat with many friends in same chat browser with multiple friends get more clear idea with the modified screen shot from google screen shot.
separate tab chatting is also a new feature Google is thinking of, which will give extra space for chatting.
this feature are not yet been introduced in Gmail labs for collecting user feedback.
the feature already introduced to public by default is that when you receive an email, and scroll your mouse over the email a window pops up allow you to chat with person.