sprang 2ddb8bd359 Avoid undefined behavior in vp8 screenshare_layers
active_layer_ could be dereferenced while being -1...
Also added som DCHECKs

BUG=webrtc:5490

Review URL: https://codereview.webrtc.org/1656233002

Cr-Commit-Position: refs/heads/master@{#11486}
2016-02-04 11:59:57 +00:00
..
2016-01-25 16:58:08 +00:00