Charts

This merge requests adds the infamous frame time graph to Mutter:

To display the chart, open the Looking Glass and run:

>>> Meta.add_clutter_debug_flags(0, Clutter.DrawDebugFlag.PAINT_FRAME_TIME, 0)

And to hide the chart, run:

>>> Meta.remove_clutter_debug_flags(0, Clutter.DrawDebugFlag.PAINT_FRAME_TIME, 0)

The line represents the maximum time slot a frame has to draw itself. If a bar crossed that line, it means the frame was missed.

It accounts for layout times (in green) and paint times (in blue).

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To Do:

• Don't disable buffer age
• Move implementation to ClutterStage
• Investigate using additional DRM planes