Adds ability to specify desired frame size separate from actual clip resolution, as well as clip and desired fps. This allows e.g. reading an HD clip but running benchmarks in VGA, and to specify e.g. 60fps for the clip but 30for encoding where frame dropping kicks in so that motion is actually correct rather than just plaing the clip slowly. Bug: webrtc:12229 Change-Id: I4ad4fcc335611a449dc2723ffafbec6731e89f55 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/195324 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Philip Eliasson <philipel@webrtc.org> Cr-Commit-Position: refs/heads/master@{#32839}