Remove ViECapture usage in VideoSendStream.

Instead a ViECapturer object is allocated and directly operated on. This
additionally exposes ViESharedData to Call to access the module
ProcessThread, moving towards Call ownership of shared resources.

BUG=1695
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45339004

Cr-Commit-Position: refs/heads/master@{#9119}
9 files changed