style: Use preferred color scheme when forcing colors with system colors (except windows HCM)

This causes (among other things) pages to be dark when using regular
windows system colors and forcing colors to "always", which is nice.

Differential Revision: https://phabricator.services.mozilla.com/D131165

components/style/gecko/media_queries.rs

@@ -14,7 +14,8 @@ use crate::media_queries::MediaType;
 use crate::properties::ComputedValues;
 use crate::string_cache::Atom;
 use crate::values::computed::font::GenericFontFamily;
-use crate::values::computed::Length;
+use crate::values::computed::{Length, ColorScheme};
+use crate::values::specified::color::SystemColor;
 use crate::values::specified::font::FONT_MEDIUM_PX;
 use crate::values::{CustomIdent, KeyframesName};
 use app_units::{Au, AU_PER_PX};
@@ -387,19 +388,28 @@ impl Device {
         self.pref_sheet_prefs().mUseDocumentColors
     }
 
+    /// Computes a system color and returns it as an nscolor.
+    pub(crate) fn system_nscolor(&self, system_color: SystemColor, color_scheme: &ColorScheme) -> u32 {
+        unsafe {
+            bindings::Gecko_ComputeSystemColor(system_color, self.document(), color_scheme)
+        }
+    }
+
     /// Returns the default background color.
     ///
     /// This is only for forced-colors/high-contrast, so looking at light colors
     /// is ok.
-    pub fn default_background_color_for_forced_colors(&self) -> RGBA {
-        convert_nscolor_to_rgba(self.pref_sheet_prefs().mLightColors.mDefaultBackground)
+    pub fn default_background_color(&self) -> RGBA {
+        let normal = ColorScheme::normal();
+        convert_nscolor_to_rgba(self.system_nscolor(SystemColor::Canvas, &normal))
     }
 
     /// Returns the default foreground color.
     ///
     /// See above for looking at light colors only.
-    pub fn default_color_for_forced_colors(&self) -> RGBA {
-        convert_nscolor_to_rgba(self.pref_sheet_prefs().mLightColors.mDefault)
+    pub fn default_color(&self) -> RGBA {
+        let normal = ColorScheme::normal();
+        convert_nscolor_to_rgba(self.system_nscolor(SystemColor::Canvastext, &normal))
     }
 
     /// Returns the current effective text zoom.

components/style/properties/cascade.rs

@@ -430,7 +430,7 @@ fn tweak_when_ignoring_colors(
             // widget background color's rgb channels but not alpha...
             let alpha = alpha_channel(color, context);
             if alpha != 0 {
-                let mut color = context.builder.device.default_background_color_for_forced_colors();
+                let mut color = context.builder.device.default_background_color();
                 color.alpha = alpha;
                 declarations_to_apply_unless_overriden
                     .push(PropertyDeclaration::BackgroundColor(color.into()))
@@ -448,7 +448,7 @@ fn tweak_when_ignoring_colors(
             // override this with a non-transparent color, then override it with
             // the default color. Otherwise just let it inherit through.
             if context.builder.get_parent_inherited_text().clone_color().alpha == 0 {
-                let color = context.builder.device.default_color_for_forced_colors();
+                let color = context.builder.device.default_color();
                 declarations_to_apply_unless_overriden.push(PropertyDeclaration::Color(
                     specified::ColorPropertyValue(color.into()),
                 ))

components/style/values/specified/color.rs

@@ -5,8 +5,6 @@
 //! Specified color values.
 
 use super::AllowQuirks;
-#[cfg(feature = "gecko")]
-use crate::gecko_bindings::structs::nscolor;
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{Color as ComputedColor, Context, ToComputedValue};
 use crate::values::generics::color::{GenericCaretColor, GenericColorOrAuto};
@@ -456,18 +454,17 @@ impl SystemColor {
     #[inline]
     fn compute(&self, cx: &Context) -> ComputedColor {
         use crate::gecko_bindings::bindings;
+        use crate::gecko::values::convert_nscolor_to_rgba;
 
         // TODO: We should avoid cloning here most likely, though it's
         // cheap-ish.
         let style_color_scheme =
             cx.style().get_inherited_ui().clone_color_scheme();
-        let color = unsafe {
-            bindings::Gecko_ComputeSystemColor(*self, cx.device().document(), &style_color_scheme)
-        };
+        let color = cx.device().system_nscolor(*self, &style_color_scheme);
         if color == bindings::NS_SAME_AS_FOREGROUND_COLOR {
             return ComputedColor::currentcolor();
         }
-        convert_nscolor_to_computedcolor(color)
+        ComputedColor::rgba(convert_nscolor_to_rgba(color))
     }
 }
 
@@ -741,12 +738,6 @@ impl Color {
     }
 }
 
-#[cfg(feature = "gecko")]
-fn convert_nscolor_to_computedcolor(color: nscolor) -> ComputedColor {
-    use crate::gecko::values::convert_nscolor_to_rgba;
-    ComputedColor::rgba(convert_nscolor_to_rgba(color))
-}
-
 impl Color {
     /// Converts this Color into a ComputedColor.
     ///