libservo: Remove Opts::webrender_stats and -Z wr-stats

[mrobinson]

This option is supported via the WebView API now and you can enable it
in servoshell by pressing Ctrl + F12. The command-line argument and
Opts field are older and I believe are no longer necessary.

Testing: This just removes a redundant command-line option, so no tests.

[mukilan]

@mrobinson there are merge conflicts in this PR. Also, is the 'Ctrl + F12' option to toggle the webrender stats documented somewhere?

[mrobinson]

@mrobinson there are merge conflicts in this PR. Also, is the 'Ctrl + F12' option to toggle the webrender stats documented somewhere?

There is currently no documentation for servoshell keybindings, so I do not think so.

[mukilan]

There is currently no documentation for servoshell keybindings, so I do not think so.

The key bindings are documented in the book. For the wr-stats option, I guess it should also be mentioned in the debugging section, I can add this, but I don't know the context e.g when this should be used etc. I'll create a separate issue to discuss this.

Ctrl+F12 is a global shortcut on my KDE desktop. I'm not sure if other platforms also map Ctrl+F12, but are we sure a command line option to toggle these debugging features will not be useful? In any case, Ctrl+F12 doesn't seem to show any WebRender stats on my machine, even after disabling the global shortcut.

[mrobinson]

Ctrl+F12 is a global shortcut on my KDE desktop. I'm not sure if other platforms also map Ctrl+F12, but are we sure a command line option to toggle these debugging features will not be useful? In any case, Ctrl+F12 doesn't seem to show any WebRender stats on my machine, even after disabling the global shortcut.

In order to see the output of this you need to enable the profiling feature and then scroll around for a while. After that, if you request a WebRender capture via the keyboard (Ctrl + F9), you should see the profiler-stats.txt file in the capture directory. I have not yet figured out how to make WebRender populate the file even though it creates it.

Since this is related to the capture functionality which is controlled by the keyboard, I'm not sure a command-line argument is the appropriate way to activate it. Perhaps we should change the shortcut key or even remove the functionality (unless we can figure out how to make it populate the file).

[mukilan]

Perhaps we should change the shortcut key or even remove the functionality (unless we can figure out how to make it populate the file).

Sounds good. Another option would be to expose this as a button in the minibrowser's toolbar or in an about:debugging page.