Separate renderer part into steps and make it easier to add more steps as separate interceptors. Bug: webrtc:10138 Change-Id: I667fc85d0da4fb59090e69caa4c32bd4afc3bd05 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/151645 Commit-Queue: Artem Titov <titovartem@webrtc.org> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29082}