Reason for revert: Seems to break VideoSendStreamTest.ReconfigureBitratesSetsEncoderBitratesCorrectly on Linux Memcheck buildbot. Original issue's description: > Work on flexible mode and screen sharing. > > Implement VP8 style screensharing but with spatial layers. > Implement flexible mode. > > Files from other patches: > generic_encoder.cc > layer_filtering_transport.cc > > BUG=webrtc:4914 > > Committed: https://crrev.com/77ccfb4d16c148e61a316746bb5d9705e8b39f4a > Cr-Commit-Position: refs/heads/master@{#10572} TBR=sprang@webrtc.org,stefan@webrtc.org,philipel@google.com,asapersson@webrtc.org,mflodman@webrtc.org,philipel@webrtc.org NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true BUG=webrtc:4914 Review URL: https://codereview.webrtc.org/1438543002 Cr-Commit-Position: refs/heads/master@{#10578}