We need to support overlays with the d3d11 video decoder.  there are some subtasks here:

- figure out what allows / prevents an overlay from being used on windows
- how do overlays interact with video processors (e.g., for color space conversion, etc.)
- same for protected content

handy links:
DC Overlays: https://cs.chromium.org/chromium/src/components/viz/service/display/dc_layer_overlay.h

where the compositor selects what to overlay from the list of quads: https://cs.chromium.org/chromium/src/components/viz/service/display/overlay_processor.cc?l=92&gs=kythe%253A%252F%252Fchromium%253Flang%253Dc%25252B%25252B%253Fpath%253Dsrc%252Fcomponents%252Fviz%252Fservice%252Fdisplay%252Foverlay_processor.cc%2523ZkXe12P8ITlD2q8e0BnM3Wbr8U9TvPDisaxYEeQBZlY%25253D&gsn=ProcessForDCLayers&ct=xref_usages

where the (old) dxva video decoder marks a video frame as being overlayable: https://cs.chromium.org/chromium/src/media/gpu/dxva_video_decode_accelerator_win.cc?rcl=92ff5ccfaf16d5e5b662be28e5d655ddccef921e&l=2218

this ends up setting a flag in the resource when it's sent to the compositor: https://cs.chromium.org/chromium/src/cc/resources/video_resource_updater.cc?rcl=92ff5ccfaf16d5e5b662be28e5d655ddccef921e&l=895

that flag is platform-independent; it just tells the compositor to consider (via the overlay processor mentioned above) overlaying this resource rather than drawing the quads that use it.