This is instead derived from pattern_idx inside the frame config. This also removes active_layer_ use from ScreenshareLayers::PopulateCodecSpecific and instead ties the layer to TemporalLayers::FrameConfig. BUG=chromium:702017, webrtc:7349 R=sprang@webrtc.org Review-Url: https://codereview.webrtc.org/2860063002 Cr-Commit-Position: refs/heads/master@{#18017}