style: Parse the legacy border attribute per the legacy HTML specification.

Additionally, this patch cleans up some miscellaneous formatting issues
and refactors files in `layout/css/` somewhat to eliminate needless
levels of indirection. It also fixes our handling of presentational
hints that only apply if border is nonzero.

components/style/selector_matching.rs

@@ -799,6 +799,13 @@ pub fn common_style_affecting_attributes() -> [CommonStyleAffectingAttributeInfo
     ]
 }
 
+/// Attributes that, if present, disable style sharing. All legacy HTML attributes must be in
+/// either this list or `common_style_affecting_attributes`. See the comment in
+/// `synthesize_presentational_hints_for_legacy_attributes`.
+pub fn rare_style_affecting_attributes() -> [Atom, ..1] {
+    [ atom!("border") ]
+}
+
 /// Determines whether the given element matches the given single selector.
 ///
 /// NB: If you add support for any new kinds of selectors to this routine, be sure to set
@@ -993,6 +1000,12 @@ pub fn matches_simple_selector<'a,E,N>(selector: &SimpleSelector,
                 matches_generic_nth_child(element, 0, 1, true, true)
         }
 
+        ServoNonzeroBorder => {
+            *shareable = false;
+            let elem = element.as_element();
+            elem.has_nonzero_border()
+        }
+
         Negation(ref negated) => {
             *shareable = false;
             !negated.iter().all(|s| matches_simple_selector(s, element, shareable))