This relates to this webrtc bug: https://bugs.chromium.org/p/webrtc/issues/detail?id=9734

We would like to merge the following CLs:
https://chromiumdash.appspot.com/commit/7461eff1bd762b6509273f5194b24e098524e692
https://chromiumdash.appspot.com/commit/661a0c6b021f5ad4efa33ed673267320c88809fa
These two alter the settings used for an additional screencast stream and is a noop unless the WebRTC-SimulcastScreenshare finch experiment is enabled.

https://chromiumdash.appspot.com/commit/f4ef2dd532692b45b77d22746e8ac407d1f35a46
This CL is extremely safe/small, it prevents us for sending incorrect metadata (indicating to the remote party that is stream is being removed) when it is really just being temporarily throttled due to limited network.

https://chromiumdash.appspot.com/commit/fb2a66a58ac3e61162804d5fcdc377e465852d2e
This change fixes an incorrect setting preventing the libvpx vp8 encoder from properly being able to adjust the encoded rate.

All of these changes are out in canary.