Auto merge of #16757 - zombiefungus:issue16716, r=KiChjang

Remove obsolete paint threads option #16716

<!-- Please describe your changes on the following line: -->
Remove paint_threads from `ports/cef/core.rs` and `components/config/opts.rs`

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #16716

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/config/opts.rs

@@ -32,11 +32,6 @@ pub struct Opts {
     /// The initial URL to load.
     pub url: Option<ServoUrl>,
 
-    /// How many threads to use for CPU painting (`-t`).
-    ///
-    /// Note that painting is sequentialized when using GPU painting.
-    pub paint_threads: usize,
-
     /// The maximum size of each tile in pixels (`-s`).
     pub tile_size: usize,
 
@@ -504,7 +499,6 @@ pub fn default_opts() -> Opts {
     Opts {
         is_running_problem_test: false,
         url: Some(ServoUrl::parse("about:blank").unwrap()),
-        paint_threads: 1,
         tile_size: 512,
         device_pixels_per_px: None,
         time_profiling: None,
@@ -693,12 +687,6 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
             .unwrap_or_else(|err| args_fail(&format!("Error parsing option: --device-pixel-ratio ({})", err)))
     );
 
-    let mut paint_threads: usize = match opt_match.opt_str("t") {
-        Some(paint_threads_str) => paint_threads_str.parse()
-            .unwrap_or_else(|err| args_fail(&format!("Error parsing option: -t ({})", err))),
-        None => cmp::max(num_cpus::get() * 3 / 4, 1),
-    };
-
     // If only the flag is present, default to a 5 second period for both profilers
     let time_profiling = if opt_match.opt_present("p") {
         match opt_match.opt_str("p") {
@@ -748,7 +736,6 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
 
     let mut bubble_inline_sizes_separately = debug_options.bubble_widths;
     if debug_options.trace_layout {
-        paint_threads = 1;
         layout_threads = Some(1);
         bubble_inline_sizes_separately = true;
     }
@@ -809,7 +796,6 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     let opts = Opts {
         is_running_problem_test: is_running_problem_test,
         url: Some(url),
-        paint_threads: paint_threads,
         tile_size: tile_size,
         device_pixels_per_px: device_pixels_per_px,
         time_profiling: time_profiling,

ports/cef/core.rs

@@ -68,7 +68,6 @@ pub extern "C" fn cef_initialize(args: *const cef_main_args_t,
     };
 
     let mut temp_opts = opts::default_opts();
-    temp_opts.paint_threads = rendering_threads;
     temp_opts.headless = false;
     temp_opts.hard_fail = false;
     temp_opts.enable_text_antialiasing = true;