Move VideoFramePump to remoting/protocol

VideoFramePump will not be used for WebRTC-based connection. In a separate
change I plan to move creation of the VideoFramePump to IceConnectionToHost
so the host layer will not need to know when VideoFramePump needs to be
used.

Review URL: https://codereview.chromium.org/1462063004

Cr-Commit-Position: refs/heads/master@{#361205}