Auto merge of #16797 - ferjm:bug1361994.mozdocument.cssom, r=xidorn

Stylo: Bug 1361994 - Implement access to CSSMozDocumentRule

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

Bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1361994

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ports/geckolib/glue.rs

@@ -28,6 +28,7 @@ use style::gecko::wrapper::GeckoElement;
 use style::gecko_bindings::bindings;
 use style::gecko_bindings::bindings::{RawGeckoKeyframeListBorrowed, RawGeckoKeyframeListBorrowedMut};
 use style::gecko_bindings::bindings::{RawServoDeclarationBlockBorrowed, RawServoDeclarationBlockStrong};
+use style::gecko_bindings::bindings::{RawServoDocumentRule, RawServoDocumentRuleBorrowed};
 use style::gecko_bindings::bindings::{RawServoMediaList, RawServoMediaListBorrowed, RawServoMediaListStrong};
 use style::gecko_bindings::bindings::{RawServoMediaRule, RawServoMediaRuleBorrowed};
 use style::gecko_bindings::bindings::{RawServoNamespaceRule, RawServoNamespaceRuleBorrowed};
@@ -88,7 +89,7 @@ use style::style_adjuster::StyleAdjuster;
 use style::stylearc::Arc;
 use style::stylesheets::{CssRule, CssRules, CssRuleType, CssRulesHelpers};
 use style::stylesheets::{ImportRule, MediaRule, NamespaceRule, Origin};
-use style::stylesheets::{PageRule, Stylesheet, StyleRule, SupportsRule};
+use style::stylesheets::{PageRule, Stylesheet, StyleRule, SupportsRule, DocumentRule};
 use style::stylesheets::StylesheetLoader as StyleStylesheetLoader;
 use style::supports::parse_condition_or_declaration;
 use style::thread_state;
@@ -839,6 +840,13 @@ impl_group_rule_funcs! { (Supports, SupportsRule, RawServoSupportsRule),
     to_css: Servo_SupportsRule_GetCssText,
 }
 
+impl_group_rule_funcs! { (Document, DocumentRule, RawServoDocumentRule),
+    get_rules: Servo_DocumentRule_GetRules,
+    getter: Servo_CssRules_GetDocumentRuleAt,
+    debug: Servo_DocumentRule_Debug,
+    to_css: Servo_DocumentRule_GetCssText,
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_CssRules_GetFontFaceRuleAt(rules: ServoCssRulesBorrowed, index: u32)
                                                    -> *mut nsCSSFontFaceRule
@@ -918,6 +926,14 @@ pub extern "C" fn Servo_SupportsRule_GetConditionText(rule: RawServoSupportsRule
     })
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_DocumentRule_GetConditionText(rule: RawServoDocumentRuleBorrowed,
+                                                      result: *mut nsAString) {
+    read_locked_arc(rule, |rule: &DocumentRule| {
+        rule.condition.to_css(unsafe { result.as_mut().unwrap() }).unwrap();
+    })
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_ComputedValues_GetForAnonymousBox(parent_style_or_null: ServoComputedValuesBorrowedOrNull,
                                                           pseudo_tag: *mut nsIAtom,