Currently Flash can request a number of rendering modes. Specifically -
https://wiki.mozilla.org/Plugins/Async_Drawing

• NPDrawingModelSyncWin - This is a synchronous rendering mode leveraged when we paint windowless plugin content. It is backed by a mozilla::gfx::SharedDIBSurface which is a GDI bitmap with a handle shared between processes.
• NPDrawingModelAsyncBitmapSurface - This is an async mode leveraged when Flash or Firefox do not support acceleration. On our end we fail to support acceleration for blocked graphics drivers. Flash may also block using acceleration for similar reason internally. It is backed by an IPDL shared memory buffer that is platform agnostic.
• NPDrawingModelAsyncWindowsDXGISurface - This is an async mode leveraged when Flash and Firefox support graphics acceleration. Firefox exposes an API that supports the creation and management of accelerated graphics memory objects which Flash paints directly to.

This bug is about killing off NPDrawingModelAsyncWindowsDXGISurface as part of shipping win32k lockdown and our Flash deprecation strategy.

FYI I filed this in anticipation of removing the async accellerated path for win32k lockdown. If we don't need to do that anymore we can resolve wontfix this.

Yep, we'll keep NPDrawingModelAsyncWindowsDXGISurface -- win32k lockdown work for it is in bug 1577336.