This cl make it possible for the hw video encoder to downscale a texture image before encoding. The purpose is to allow downscaling if the quality is too bad at the current resolution. BUG=webrtc:4993 R=magjed@webrtc.org, pbos@webrtc.org Review URL: https://codereview.webrtc.org/1470043002 . Cr-Commit-Position: refs/heads/master@{#10804}