Revert "media/gpu: a bit of folder cleanup"

This reverts commit 1e14f8a0183561052b1ee461f530f7b854ec18dd.

Reason for revert: broke Win7 bot
Bug: 944748

Original change's description:
> media/gpu: a bit of folder cleanup
> 
> This CL moves around a few files in ///media/gpu:
> - moves media/gpu/fake_video_decode_accelerator.* to media/gpu/test
>   since it's only used from media/gpu/video_decode_accelerator_unittest.cc.
> - moves media/gpu/fake_command_buffer_helper.* to media/gpu/test since
>   it's only used in unit tests.
> - moves the media/gpu/vt_video* files to media/gpu/mac to follow the
>   other platform-specific files around.
> 
> No new functionality intended, just moving things around. I stumbled
> upon these oddities while renaming JpegDecodeAccelerator to Mjpeg...
> things.
> 
> Bug: 932860
> Change-Id: Ibf2b2c70c7afca6834385c0db7b51d116d505b38
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535003
> Commit-Queue: Miguel Casas <mcasas@chromium.org>
> Commit-Queue: Robert Sesek <rsesek@chromium.org>
> Auto-Submit: Miguel Casas <mcasas@chromium.org>
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Dan Sanders <sandersd@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#643207}

TBR=mcasas@chromium.org,sandersd@chromium.org,rsesek@chromium.org

Change-Id: I0207c5df5831d2d6aed9a9430cf73bd076a47a31
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 932860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535997
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643337}
16 files changed