Backed out changeset 10a9a5639f09 (bug 1812498) for various shutdown hangs.

dom/media/ipc/RDDProcessManager.cpp

dom/media/ipc/RDDProcessManager.h

dom/media/ipc/RemoteDecoderManagerParent.cpp

gfx/ipc/GPUParent.cpp

gfx/layers/composite/TextureHost.cpp

gfx/layers/composite/TextureHost.h

gfx/layers/ipc/CompositorThread.cpp

gfx/layers/ipc/VideoBridgeParent.cpp

gfx/layers/ipc/VideoBridgeParent.h

gfx/thebes/gfxPlatform.cpp

gfx/webrender_bindings/RenderBufferTextureHost.cpp

gfx/webrender_bindings/RenderBufferTextureHost.h

gfx/webrender_bindings/RenderTextureHost.cpp

gfx/webrender_bindings/RenderTextureHost.h

gfx/webrender_bindings/RenderThread.cpp

gfx/webrender_bindings/RenderThread.h