The idea here is to be able to visualize and immediately
understand what is happening. Something like:
```
[ view1 ] [ view2 ]
[---- Layout ---][------ Paint ------][ Pick ]
[================== Update =====================]
```
But with colors. A few of the previous profiling data
sections were removed, since they didn't really add to
reading the graph.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/197
Add the ability to add tracing instrumentation to the code. When
enabled, trace entries will generate a file with timing information
that will be processable by sysprof for generating visualization of
traces over time.
While enabled by default at compile time, it is possible to disable the
expansion of the macros completely by passing --disable-tracing to
./configure.
Tracing is so far only actually done if actually enabled on explicitly
specified threads.
This will be used by Mutter passing the write end of a pipe, where the
read end is sent to Sysprof itself via the D-Bus method 'Capture()'.
By passing that, we have to detect EPIPE that is sent when Sysprof stops
recording. Fortunately, we already ignore the signal at meta_init(), so
no need to add a custom signal handler.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/197
