Virtual input devices aim to enable injecting input events as if they
came from hardware events. This is useful for things such as remote
controlling, for example via a remote desktop session.
The API so far only consists of stumps.
https://bugzilla.gnome.org/show_bug.cgi?id=765009
CoglFrameInfo is a frame info container associated with a single
onscreen framebuffer. The clutter stage will eventually support drawing
a stage frame with multiple onscreen framebuffers, thus needs its own
frame info container.
This patch introduces a new stage signal 'presented' and a accompaning
ClutterFrameInfo and adapts the stage windows and past onscreen frame
callbacks users to use the signal and new info container.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
