Make ChildrenIterator concrete.

This will allow us to specialize ChildrenIterator in the Gecko case to do
something more interesting in some cases.

components/script/layout_wrapper.rs

@@ -115,6 +115,7 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
     type ConcreteElement = ServoLayoutElement<'ln>;
     type ConcreteDocument = ServoLayoutDocument<'ln>;
     type ConcreteRestyleDamage = RestyleDamage;
+    type ConcreteChildrenIterator = ServoChildrenIterator<'ln>;
 
     fn to_unsafe(&self) -> UnsafeNode {
         unsafe {
@@ -147,6 +148,12 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
         self.dump_style_indent(0);
     }
 
+    fn children(self) -> ServoChildrenIterator<'ln> {
+        ServoChildrenIterator {
+            current: self.first_child(),
+        }
+    }
+
     fn opaque(&self) -> OpaqueNode {
         unsafe { self.get_jsmanaged().opaque() }
     }
@@ -280,6 +287,19 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
     }
 }
 
+pub struct ServoChildrenIterator<'a> {
+    current: Option<ServoLayoutNode<'a>>,
+}
+
+impl<'a> Iterator for ServoChildrenIterator<'a> {
+    type Item = ServoLayoutNode<'a>;
+    fn next(&mut self) -> Option<ServoLayoutNode<'a>> {
+        let node = self.current;
+        self.current = node.and_then(|node| node.next_sibling());
+        node
+    }
+}
+
 impl<'ln> LayoutNode for ServoLayoutNode<'ln> {
     type ConcreteThreadSafeLayoutNode = ServoThreadSafeLayoutNode<'ln>;
 

components/style/dom.rs

@@ -68,6 +68,7 @@ pub trait TNode : Sized + Copy + Clone {
     type ConcreteElement: TElement<ConcreteNode = Self, ConcreteDocument = Self::ConcreteDocument>;
     type ConcreteDocument: TDocument<ConcreteNode = Self, ConcreteElement = Self::ConcreteElement>;
     type ConcreteRestyleDamage: TRestyleDamage;
+    type ConcreteChildrenIterator: Iterator<Item = Self>;
 
     fn to_unsafe(&self) -> UnsafeNode;
     unsafe fn from_unsafe(n: &UnsafeNode) -> Self;
@@ -84,11 +85,7 @@ pub trait TNode : Sized + Copy + Clone {
     fn dump_style(self);
 
     /// Returns an iterator over this node's children.
-    fn children(self) -> ChildrenIterator<Self> {
-        ChildrenIterator {
-            current: self.first_child(),
-        }
-    }
+    fn children(self) -> Self::ConcreteChildrenIterator;
 
     /// Converts self into an `OpaqueNode`.
     fn opaque(&self) -> OpaqueNode;
@@ -244,17 +241,3 @@ pub trait TElement : PartialEq + Debug + Sized + Copy + Clone + ElementExt + Pre
         }
     }
 }
-
-pub struct ChildrenIterator<ConcreteNode> where ConcreteNode: TNode {
-    current: Option<ConcreteNode>,
-}
-
-impl<ConcreteNode> Iterator for ChildrenIterator<ConcreteNode>
-                            where ConcreteNode: TNode {
-    type Item = ConcreteNode;
-    fn next(&mut self) -> Option<ConcreteNode> {
-        let node = self.current;
-        self.current = node.and_then(|node| node.next_sibling());
-        node
-    }
-}

ports/geckolib/wrapper.rs

@@ -134,6 +134,7 @@ impl<'ln> TNode for GeckoNode<'ln> {
     type ConcreteDocument = GeckoDocument<'ln>;
     type ConcreteElement = GeckoElement<'ln>;
     type ConcreteRestyleDamage = GeckoRestyleDamage;
+    type ConcreteChildrenIterator = GeckoChildrenIterator<'ln>;
 
     fn to_unsafe(&self) -> UnsafeNode {
         (self.node as usize, 0)
@@ -163,6 +164,12 @@ impl<'ln> TNode for GeckoNode<'ln> {
         unimplemented!()
     }
 
+    fn children(self) -> GeckoChildrenIterator<'ln> {
+        GeckoChildrenIterator {
+            current: self.first_child(),
+        }
+    }
+
     fn opaque(&self) -> OpaqueNode {
         let ptr: uintptr_t = self.node as uintptr_t;
         OpaqueNode(ptr)
@@ -341,6 +348,19 @@ impl<'ln> TNode for GeckoNode<'ln> {
     unsafe fn set_dirty_on_viewport_size_changed(&self) {}
 }
 
+pub struct GeckoChildrenIterator<'a> {
+    current: Option<GeckoNode<'a>>,
+}
+
+impl<'a> Iterator for GeckoChildrenIterator<'a> {
+    type Item = GeckoNode<'a>;
+    fn next(&mut self) -> Option<GeckoNode<'a>> {
+        let node = self.current;
+        self.current = node.and_then(|node| node.next_sibling());
+        node
+    }
+}
+
 #[derive(Clone, Copy)]
 pub struct GeckoDocument<'ld> {
     document: *mut RawGeckoDocument,