GitLab

This CL removes the usage of the GpuMemoryBufferFactory from the
VaapiVideoEncodeAccelerator. This is because the GMB factory is not
really needed to allocate buffers and not having it simplifies things.

Note that we must start the |encoder_task_runner_| with base::MayBlock()
because the first encoder to make use of this path will open the render
node.

Bug: b:173167846
Test: video.EncodeAccel.h264_720p_nv12_dmabuf on atlas
Change-Id: Iafa78e7027d65182408416cba2ad6f997b24c299
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568549
Commit-Queue: Andres Calderon Jaramillo <andrescj@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835366}