Backed out changeset fc813bf68348 for failing reftest layout/reftests/bugs/272646-1.xul on OS X. r=backout

Backs out https://github.com/servo/servo/pull/19045

components/style/sharing/checks.rs

@@ -6,6 +6,7 @@
 //! quickly whether it's worth to share style, and whether two different
 //! elements can indeed share the same style.
 
+use Atom;
 use bloom::StyleBloom;
 use context::{SelectorFlagsMap, SharedStyleContext};
 use dom::TElement;
@@ -95,16 +96,14 @@ pub fn have_same_class<E>(target: &mut StyleSharingTarget<E>,
 /// :first-child, etc, or on attributes that we don't check off-hand (pretty
 /// much every attribute selector except `id` and `class`.
 #[inline]
-pub fn revalidate<E>(
-    target: &mut StyleSharingTarget<E>,
-    candidate: &mut StyleSharingCandidate<E>,
-    shared_context: &SharedStyleContext,
-    bloom: &StyleBloom<E>,
-    nth_index_cache: &mut NthIndexCache,
-    selector_flags_map: &mut SelectorFlagsMap<E>,
-) -> bool
-where
-    E: TElement,
+pub fn revalidate<E>(target: &mut StyleSharingTarget<E>,
+                     candidate: &mut StyleSharingCandidate<E>,
+                     shared_context: &SharedStyleContext,
+                     bloom: &StyleBloom<E>,
+                     nth_index_cache: &mut NthIndexCache,
+                     selector_flags_map: &mut SelectorFlagsMap<E>)
+                     -> bool
+    where E: TElement,
 {
     let stylist = &shared_context.stylist;
 
@@ -131,25 +130,16 @@ where
 
 /// Checks whether we might have rules for either of the two ids.
 #[inline]
-pub fn may_match_different_id_rules<E>(
-    shared_context: &SharedStyleContext,
-    element: E,
-    candidate: E,
-) -> bool
-where
-    E: TElement,
+pub fn may_have_rules_for_ids(shared_context: &SharedStyleContext,
+                              element_id: Option<&Atom>,
+                              candidate_id: Option<&Atom>) -> bool
 {
-    let element_id = element.get_id();
-    let candidate_id = candidate.get_id();
-
-    if element_id == candidate_id {
-        return false;
-    }
-
+    // We shouldn't be called unless the ids are different.
+    debug_assert!(element_id.is_some() || candidate_id.is_some());
     let stylist = &shared_context.stylist;
 
     let may_have_rules_for_element = match element_id {
-        Some(ref id) => stylist.may_have_rules_for_id(id, element),
+        Some(id) => stylist.may_have_rules_for_id(id),
         None => false
     };
 
@@ -158,7 +148,7 @@ where
     }
 
     match candidate_id {
-        Some(ref id) => stylist.may_have_rules_for_id(id, candidate),
+        Some(id) => stylist.may_have_rules_for_id(id),
         None => false
     }
 }