This CL makes ViEFrameCallback::DeliverFrame const and removes the potential frame copy in ViEFrameProviderBase by moving it to ViEEncoder::DeliverFrame instead, for clients that use the FrameCallback functionality to modify the frame content. BUG=1128 R=mflodman@webrtc.org Review URL: https://webrtc-codereview.appspot.com/43949004 Cr-Commit-Position: refs/heads/master@{#8934}