Introduce a get_colspan method on LayoutJS<Element>.

components/layout/table_cell.rs

@@ -20,7 +20,6 @@ use model::MaybeAuto;
 use std::fmt;
 use std::sync::Arc;
 use style::computed_values::{border_collapse, border_top_style};
-use style::legacy::UnsignedIntegerAttribute;
 use style::properties::ComputedValues;
 use table::InternalTable;
 use table_row::{CollapsedBorder, CollapsedBorderProvenance};
@@ -52,8 +51,7 @@ impl TableCellFlow {
         TableCellFlow {
             block_flow: BlockFlow::from_fragment(fragment, None),
             collapsed_borders: CollapsedBordersForCell::new(),
-            column_span: node.get_unsigned_integer_attribute(UnsignedIntegerAttribute::ColSpan)
+            column_span: node.get_colspan(),
-                             .unwrap_or(1),
             visible: visible,
         }
     }

components/layout/wrapper.rs

@@ -1039,6 +1039,12 @@ impl<'ln> ThreadSafeLayoutNode<'ln> {
             iframe_element.pipeline_id().unwrap()
         }
     }
+
+    pub fn get_colspan(&self) -> u32 {
+        unsafe {
+            self.get_jsmanaged().downcast::<Element>().unwrap().get_colspan()
+        }
+    }
 }
 
 pub struct ThreadSafeLayoutNodeChildrenIterator<'a> {

components/script/dom/element.rs

@@ -225,6 +225,8 @@ pub trait LayoutElementHelpers {
     unsafe fn synthesize_presentational_hints_for_legacy_attributes<V>(&self, &mut V)
         where V: VecLike<DeclarationBlock<Vec<PropertyDeclaration>>>;
     #[allow(unsafe_code)]
+    unsafe fn get_colspan(self) -> u32;
+    #[allow(unsafe_code)]
     unsafe fn get_unsigned_integer_attribute_for_layout(&self, attribute: UnsignedIntegerAttribute)
                                                         -> Option<u32>;
     #[allow(unsafe_code)]
@@ -499,6 +501,17 @@ impl LayoutElementHelpers for LayoutJS<Element> {
         }
     }
 
+    #[allow(unsafe_code)]
+    unsafe fn get_colspan(self) -> u32 {
+        if let Some(this) = self.downcast::<HTMLTableCellElement>() {
+            this.get_colspan().unwrap_or(1)
+        } else {
+            // Don't panic since `display` can cause this to be called on arbitrary
+            // elements.
+            1
+        }
+    }
+
     #[allow(unsafe_code)]
     unsafe fn get_unsigned_integer_attribute_for_layout(&self,
                                                         attribute: UnsignedIntegerAttribute)