This change replaces all GetWindowList / GetScreenList with GetScreenList,
SelectWindow / SelectScreen with SelectSource, and BringSelectedWindowToFront
with FocusOnSelectedSource in WebRTC.
BUG=webrtc:6513
Review-Url: https://codereview.webrtc.org/2479553006
Cr-Commit-Position: refs/heads/master@{#14960}