Debug flag for SHOW_FPS
This MR is based on the SHOW_FPS update in !154 (merged) and adds an updated version of a patch in !502 (closed) to it. It should not be merged before !154 (merged).
The CLUTTER_SHOW_FPS env var is converted into a CLUTTER_DEBUG flag. This makes it runtime settable and brings it closer to the other debugging options.
CLUTTER_DEBUG=frame-time
replaces the old CLUTTER_SHOW_FPS=1
.
Meta.add_clutter_debug_flags(Clutter.DebugFlag.FRAME_TIME, 0, 0)
enables it at runtime.
I had abandoned this branch as it seemed that sysprof would take over this responsibility. From a recent blog post it seems that there is still plans to use it though. So here is what I had locally. If we choose to keep the SHOW_FPS around then it will be a bit more user friendly.