Chrome Version       : 51.0.2704.103
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari: untested
    Firefox: FAIL (but in a different way)
         IE: untested

What steps will reproduce the problem?
(1) Attach an external monitor (like a physical screen) and have the additional monitor mirror the primary screen (as opposed to extending the desktop)
(2) Start some sort of webrtc screenshare, and share the screen
(3) Unplug the external monitor

What is the expected result?
I would expect the webrtc source to be the same and to be able to continue sharing

What happens instead?
The media stream source is closed, and I need to create a new one (including having the user select a source again)

Please provide any additional information below. Attach a screenshot if
possible.