Bug 1828183 - Remove cascade layers pref. r=CanadaHonk

These have been enabled by default for quite a while.

Differential Revision: https://phabricator.services.mozilla.com/D175513

dom/webidl/CSSImportRule.webidl

@@ -23,6 +23,5 @@ interface CSSImportRule : CSSRule {
 
 // https://drafts.csswg.org/css-cascade-5/#extensions-to-cssimportrule-interface
 partial interface CSSImportRule {
-  [Pref="layout.css.cascade-layers.enabled"]
   readonly attribute UTF8String? layerName;
 };

dom/webidl/CSSLayerBlockRule.webidl

@@ -6,7 +6,7 @@
  * The origin of this IDL file is
  * https://drafts.csswg.org/css-cascade-5/#the-csslayerblockrule-interface
  */
-[Exposed=Window, Pref="layout.css.cascade-layers.enabled"]
+[Exposed=Window]
 interface CSSLayerBlockRule : CSSGroupingRule {
   readonly attribute UTF8String name;
 };

dom/webidl/CSSLayerStatementRule.webidl

@@ -6,7 +6,7 @@
  * The origin of this IDL file is
  * https://drafts.csswg.org/css-cascade-5/#the-csslayerstatementrule-interface
  */
-[Exposed=Window, Pref="layout.css.cascade-layers.enabled"]
+[Exposed=Window]
 interface CSSLayerStatementRule : CSSRule {
   // readonly attribute FrozenArray<CSSOMString> nameList;
   [Frozen, Cached, Pure]

modules/libpref/init/StaticPrefList.yaml

@@ -8224,13 +8224,6 @@
   value: -1
   mirror: always
 
-# Whether @layer is enabled
-- name: layout.css.cascade-layers.enabled
-  type: RelaxedAtomicBool
-  value: true
-  mirror: always
-  rust: true
-
 # Whether Container Queries are enabled
 - name: layout.css.container-queries.enabled
   type: RelaxedAtomicBool

servo/components/style/properties/properties.mako.rs

@@ -1191,7 +1191,7 @@ impl CSSWideKeyword {
             "inherit" => CSSWideKeyword::Inherit,
             "unset" => CSSWideKeyword::Unset,
             "revert" => CSSWideKeyword::Revert,
-            "revert-layer" if static_prefs::pref!("layout.css.cascade-layers.enabled") => CSSWideKeyword::RevertLayer,
+            "revert-layer" => CSSWideKeyword::RevertLayer,
             _ => return Err(()),
         })
     }

servo/components/style/stylesheets/rule_parser.rs

@@ -259,9 +259,7 @@ impl<'a, 'i> AtRuleParser<'i> for TopLevelRuleParser<'a> {
                     }).ok()
                 };
 
-                let layer = if !static_prefs::pref!("layout.css.cascade-layers.enabled") {
-                    None
-                } else if input.try_parse(|input| input.expect_ident_matching("layer")).is_ok() {
+                let layer = if input.try_parse(|input| input.expect_ident_matching("layer")).is_ok() {
                     Some(ImportLayer {
                         name: None,
                     })
@@ -495,7 +493,7 @@ impl<'a, 'b, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'b> {
                 let condition = Arc::new(ContainerCondition::parse(self.context, input)?);
                 AtRulePrelude::Container(condition)
             },
-            "layer" if static_prefs::pref!("layout.css.cascade-layers.enabled") => {
+            "layer" => {
                 let names = input.try_parse(|input| {
                     input.parse_comma_separated(|input| {
                         LayerName::parse(self.context, input)

testing/web-platform/meta/css/__dir__.ini

@@ -1 +1 @@
-prefs: [dom.animations-api.compositing.enabled:true,layout.css.cascade-layers.enabled:true]
+prefs: [dom.animations-api.compositing.enabled:true]