Auto merge of #17912 - bzbarsky:stylo-first-line, r=emilio

Implement ::first-line support in stylo

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Fixes Gecko bug 1324619.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1324619

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because there are Gecko tests

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components/style/gecko/data.rs

@@ -204,6 +204,15 @@ impl PerDocumentStyleDataImpl {
     pub fn clear_stylist(&mut self) {
         self.stylist.clear();
     }
+
+    /// Returns whether visited links are enabled.
+    fn visited_links_enabled(&self) -> bool {
+        unsafe { bindings::Gecko_AreVisitedLinksEnabled() }
+    }
+    /// Returns whether visited styles are enabled.
+    pub fn visited_styles_enabled(&self) -> bool {
+        self.visited_links_enabled() && !self.is_private_browsing_enabled()
+    }
 }
 
 unsafe impl HasFFI for PerDocumentStyleData {

components/style/gecko/generated/bindings.rs

@@ -2817,6 +2817,16 @@ extern "C" {
                                     set: RawServoStyleSetBorrowed)
      -> ServoStyleContextStrong;
 }
+extern "C" {
+    pub fn Servo_ReparentStyle(style_to_reparent: ServoStyleContextBorrowed,
+                               parent_style: ServoStyleContextBorrowed,
+                               parent_style_ignoring_first_line:
+                                   ServoStyleContextBorrowed,
+                               layout_parent_style: ServoStyleContextBorrowed,
+                               element: RawGeckoElementBorrowedOrNull,
+                               set: RawServoStyleSetBorrowed)
+     -> ServoStyleContextStrong;
+}
 extern "C" {
     pub fn Servo_TraverseSubtree(root: RawGeckoElementBorrowed,
                                  set: RawServoStyleSetBorrowed,

components/style/gecko/pseudo_element.rs

@@ -87,6 +87,12 @@ impl PseudoElement {
         *self == PseudoElement::FirstLetter
     }
 
+    /// Whether this pseudo-element is ::first-line.
+    #[inline]
+    pub fn is_first_line(&self) -> bool {
+        *self == PseudoElement::FirstLine
+    }
+
     /// Whether this pseudo-element is ::-moz-fieldset-content.
     #[inline]
     pub fn is_fieldset_content(&self) -> bool {