servoshell: Do not override HiDPI ratio when taking screenshots (#39501)

This override is meant to force reftests to always run with a device
pixel ratio of 1.0. Reftests are always run in headless mode which uses
a device pixel ratio of 1.0 regardless (unless you override it).
Removing this particular override allows taking screenshots in the
system DPI when taking them in headed mode, which is actually a bit
useful.

Testing: A test verifying the old behavior is removed. This causes 
`/css/pixel_snapping_position_a.html` to start passing.

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

ports/servoshell/prefs.rs

@@ -645,12 +645,6 @@ pub(crate) fn parse_command_line_arguments(args: Vec<String>) -> ArgumentParsing
         preferences.js_ion_enabled = false;
     }
 
-    let device_pixel_ratio_override = if cmd_args.output.is_some() {
-        Some(1.0)
-    } else {
-        cmd_args.device_pixel_ratio
-    };
-
     // 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 = cmd_args
@@ -662,7 +656,7 @@ pub(crate) fn parse_command_line_arguments(args: Vec<String>) -> ArgumentParsing
     let servoshell_preferences = ServoShellPreferences {
         url: Some(cmd_args.url),
         no_native_titlebar: cmd_args.no_native_titlebar,
-        device_pixel_ratio_override,
+        device_pixel_ratio_override: cmd_args.device_pixel_ratio,
         clean_shutdown: cmd_args.clean_shutdown,
         headless: cmd_args.headless,
         tracing_filter: cmd_args.tracing_filter,
@@ -881,11 +875,6 @@ fn test_profiling_args() {
 
 #[test]
 fn test_servoshell_cmd() {
-    assert_eq!(
-        test_parse("-o foo.png").2.device_pixel_ratio_override,
-        Some(1.0)
-    );
-
     assert_eq!(
         test_parse("--screen-size=1000x1000")
             .2

tests/wpt/mozilla/meta/css/pixel_snapping_position_a.html.ini

@@ -1,2 +0,0 @@
-[pixel_snapping_position_a.html]
-  expected: FAIL