Note this is different to #7281 as this is dealing with automatic reporting of incoming messages from within an already active chat window, rather than a global notification.

Steps to reproduce:

With NVDA running:

1. Start Skype for Business 2016 on two separate machines, logged into separate accounts with the same organisation
2. From machine A: Find the account logged into on machine B, and type a message to that account.

Expected behavior:
NVDA should report the new message as it appears in the chat history, on both machines.

Actual behavior:
NVDA reports nothing at all.

Technical info:
Skype for business fires a liveRegionChanged UIAutomation event on each new message. Therefore NVDA should support UIA live region events in general... which will be useful also in places such as when no results are available when searching in settings, the MS Edge notification bar, and Windows update progress on the logon screen.
However, Skype for Business has a strange implementation where it concatinates recent messages (from the same person and same minute) into one message. Therefore Some custom code for Skype for business will also be needed here.