servoshell: Allow overriding screen resolution with a command-line argument (#34038)

There is a command-line argument to override the default window size,
but not one for overriding the default screen resolution. This is
important for testing pages that use screen size to have different
behavior.

In addition to adding the new option this change:

 - Renames the `--resolution` command-line argument to `--window-size`
   to remove ambiguity with the `--screen-size` argument.
 - Passes the screen size as device independent (device pixels scaled by
   HiDPI factor) to Servo internals. Not only it make it simpler to pass
   the `--window-size` override, it makes more sense. Different screens
   can have different HiDPI factors and these can be different from the
   scale of the window. This makes the screen HiDPI factor totally
   independent of the one that Servo uses for the window.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/config/opts.rs

@@ -83,6 +83,10 @@ pub struct Opts {
     /// The initial requested size of the window.
     pub initial_window_size: Size2D<u32, DeviceIndependentPixel>,
 
+    /// An override for the screen resolution. This is useful for testing behavior on different screen sizes,
+    /// such as the screen of a mobile device.
+    pub screen_size_override: Option<Size2D<u32, DeviceIndependentPixel>>,
+
     /// Whether we're running in multiprocess mode.
     pub multiprocess: bool,
 
@@ -410,6 +414,7 @@ pub fn default_opts() -> Opts {
         devtools_server_enabled: false,
         webdriver_port: None,
         initial_window_size: Size2D::new(1024, 740),
+        screen_size_override: None,
         multiprocess: false,
         background_hang_monitor: false,
         random_pipeline_closure_probability: None,
@@ -503,7 +508,18 @@ pub fn from_cmdline_args(mut opts: Options, args: &[String]) -> ArgumentParsingR
         "Start remote WebDriver server on port",
         "7000",
     );
-    opts.optopt("", "resolution", "Set window resolution.", "1024x740");
+    opts.optopt(
+        "",
+        "window-size",
+        "Set the initial window size in logical (device independenrt) pixels",
+        "1024x740",
+    );
+    opts.optopt(
+        "",
+        "screen-size",
+        "Override the screen resolution in logical (device independent) pixels",
+        "1024x768",
+    );
     opts.optflag("M", "multiprocess", "Run in multiprocess mode");
     opts.optflag("B", "bhm", "Background Hang Monitor enabled");
     opts.optflag("S", "sandbox", "Run in a sandbox if multiprocess");
@@ -694,21 +710,33 @@ pub fn from_cmdline_args(mut opts: Options, args: &[String]) -> ArgumentParsingR
         })
     });
 
-    let initial_window_size = match opt_match.opt_str("resolution") {
-        Some(res_string) => {
-            let res: Vec<u32> = res_string
-                .split('x')
-                .map(|r| {
-                    r.parse().unwrap_or_else(|err| {
-                        args_fail(&format!("Error parsing option: --resolution ({})", err))
-                    })
+    let parse_resolution_string = |string: String| {
+        let components: Vec<u32> = string
+            .split('x')
+            .map(|component| {
+                component.parse().unwrap_or_else(|error| {
+                    args_fail(&format!("Error parsing resolution '{string}': {error}"));
                 })
-                .collect();
-            Size2D::new(res[0], res[1])
-        },
-        None => Size2D::new(1024, 740),
+            })
+            .collect();
+        Size2D::new(components[0], components[1])
     };
 
+    let screen_size_override = opt_match
+        .opt_str("screen-size")
+        .map(parse_resolution_string);
+
+    // Make sure the default window size is not larger than any provided screen size.
+    let default_window_size = Size2D::new(1024, 740);
+    let default_window_size = screen_size_override
+        .map_or(default_window_size, |screen_size_override| {
+            default_window_size.min(screen_size_override)
+        });
+
+    let initial_window_size = opt_match
+        .opt_str("window-size")
+        .map_or(default_window_size, parse_resolution_string);
+
     if opt_match.opt_present("M") {
         MULTIPROCESS.store(true, Ordering::SeqCst)
     }
@@ -753,6 +781,7 @@ pub fn from_cmdline_args(mut opts: Options, args: &[String]) -> ArgumentParsingR
         devtools_server_enabled,
         webdriver_port,
         initial_window_size,
+        screen_size_override,
         multiprocess: opt_match.opt_present("M"),
         background_hang_monitor: opt_match.opt_present("B"),
         sandbox: opt_match.opt_present("S"),