[wpe-2.38] Add ftrace based system tracing

[asurdej-comcast]

[wpe-2.38] Add ftrace based system tracing

Add WebKit tracing with linux 'ftrace' that can be used on STB devices.
Write tracing points into 'trace_marker' file with 'perfetto'
compatible format.
The results can be collected and visualized by 'perfetto'

Quite similar to what is available in 2.46 with sysprof but ftrace can be used directly on the device (ftrace needs to be enabled in kernel). This is initial version to discuss, probably needs to be extended with more tracing points/scopes to mark painting, compositing, etc

fe50f1a

Build-Tests	Layout-Tests
✅ 🛠 wpe-238-amd64-build	✅ 🧪 wpe-238-amd64-layout
✅ 🛠 wpe-238-arm32-build	✅ 🧪 wpe-238-arm32-layout

[asurdej-comcast]

Simple preview of what can we see with perfetto. There are not many tracing points in 2.38 currently but probably we can add more later. There will be more for sure with 2.46

[pgorszkowski-igalia]

@asurdej-comcast : may I ask why you want to have ftrace instead of backporting the change with sysprof?

[asurdej-comcast]

@pgorszkowski-igalia We've been playing with ftrace for some time and it is supported on our devices. Also perfetto can use ftrace as data source so we can track webkit with CPU scheduling, etc at once

Regarding sysprof, I just had a quick look and my impresion was it is intended to be used in gtk/pc environment, but I can be wrong heare. Is there any simple way to run it directly on STB device? If so then we can definitely try it

[pgorszkowski-igalia]

@asurdej-comcast : in theory it should be possible to use sysprof(actually muprof: https://gitlab.gnome.org/feaneron/muprof/) on any linux device, we have never tested it with RPi or other devices. Currently it is available on 2.46 so I will try to run wpe-2.46 with muprof on RPi and if it works I will let you know.
Some documentation about integration WebKit with sysprof you can read: WebKit/WebKit#29681