Do not run faster than 60 FPS

[paulrouget]

Fix #25305

[atouchet]

Does this limit Servo to running at 60 FPS? Would it make sense to instead use the display's refresh rate?

[paulrouget]

If the monitor is cadenced at 120 FPS, it will force Servo to run at 60 FPS.

We could rely on https://docs.rs/winit/0.20.0-alpha4/winit/monitor/struct.VideoMode.html#method.refresh_rate

We should also maybe only sleep if no call to compositor::composite happen.

This is an improvement non the less.

[atouchet]

If the monitor is cadenced at 120 FPS, it will force Servo to run at 60 FPS.

What about displays that don't run at multiples of 60 (ex. 75, 90, 144, etc.)?

[paulrouget]

Servo will always run at 60FPS max.

This is not the best approach. Open to suggestions.

[atouchet]

Using that winit method instead of assuming 60 seems like a reasonable idea to me.

[Manishearth]

cc @asajeffrey thoughts on this?

[Manishearth]

Approach seems fine by me but I'm not sure if this is the right way to do this.

[asajeffrey]

Can we avoid blocking the main thread? The embedder may have things they want to do on the main thread at more than 60fps. If nothing else we should make the number 60 configurable, e.g. for devices that run at 120fps.

[paulrouget]

Closing this as this is starting to look more complex that I initially imagined. See #25305.