style: expose methods to get ::before, ::after, and the other NAC.

Reviewed-By: heycam
Bug: 1371130

MozReview-Commit-ID: JVeQevmjI3j

components/style/dom.rs

@@ -332,6 +332,23 @@ pub trait TElement : Eq + PartialEq + Debug + Hash + Sized + Copy + Clone +
         self.parent_element()
     }
 
+    /// The ::before pseudo-element of this element, if it exists.
+    fn before_pseudo_element(&self) -> Option<Self> {
+        None
+    }
+
+    /// The ::after pseudo-element of this element, if it exists.
+    fn after_pseudo_element(&self) -> Option<Self> {
+        None
+    }
+
+    /// Execute `f` for each anonymous content child (apart from ::before and
+    /// ::after) whose originating element is `self`.
+    fn each_anonymous_content_child<F>(&self, _f: F)
+    where
+        F: FnMut(Self),
+    {}
+
     /// For a given NAC element, return the closest non-NAC ancestor, which is
     /// guaranteed to exist.
     fn closest_non_native_anonymous_ancestor(&self) -> Option<Self> {

components/style/gecko/wrapper.rs

@@ -557,6 +557,25 @@ impl<'le> GeckoElement<'le> {
         self.as_node().get_bool_flag(nsINode_BooleanFlag::ElementMayHaveClass)
     }
 
+    #[inline]
+    fn has_properties(&self) -> bool {
+        use gecko_bindings::structs::NODE_HAS_PROPERTIES;
+
+        (self.flags() & NODE_HAS_PROPERTIES as u32) != 0
+    }
+
+    #[inline]
+    fn get_before_or_after_pseudo(&self, is_before: bool) -> Option<Self> {
+        if !self.has_properties() {
+            return None;
+        }
+
+        unsafe {
+            bindings::Gecko_GetBeforeOrAfterPseudo(self.0, is_before)
+                .map(GeckoElement)
+        }
+    }
+
     #[inline]
     fn may_have_style_attribute(&self) -> bool {
         self.as_node().get_bool_flag(nsINode_BooleanFlag::ElementMayHaveStyle)
@@ -689,6 +708,40 @@ impl<'le> TElement for GeckoElement<'le> {
         }
     }
 
+    fn before_pseudo_element(&self) -> Option<Self> {
+        self.get_before_or_after_pseudo(/* is_before = */ true)
+    }
+
+    fn after_pseudo_element(&self) -> Option<Self> {
+        self.get_before_or_after_pseudo(/* is_before = */ false)
+    }
+
+    /// Execute `f` for each anonymous content child element (apart from
+    /// ::before and ::after) whose originating element is `self`.
+    fn each_anonymous_content_child<F>(&self, mut f: F)
+    where
+        F: FnMut(Self),
+    {
+        let array: *mut structs::nsTArray<*mut nsIContent> =
+            unsafe { bindings::Gecko_GetAnonymousContentForElement(self.0) };
+
+        if array.is_null() {
+            return;
+        }
+
+        for content in unsafe { &**array } {
+            let node = GeckoNode::from_content(unsafe { &**content });
+            let element = match node.as_element() {
+                Some(e) => e,
+                None => continue,
+            };
+
+            f(element);
+        }
+
+        unsafe { bindings::Gecko_DestroyAnonymousContentList(array) };
+    }
+
     fn closest_non_native_anonymous_ancestor(&self) -> Option<Self> {
         debug_assert!(self.is_native_anonymous());
         let mut parent = match self.parent_element() {
@@ -868,6 +921,10 @@ impl<'le> TElement for GeckoElement<'le> {
             return None;
         }
 
+        if !self.has_properties() {
+            return None;
+        }
+
         let pseudo_type =
             unsafe { bindings::Gecko_GetImplementedPseudo(self.0) };
         PseudoElement::from_pseudo_type(pseudo_type)