style: Pass old ComputedValues and old cached struct bits to Gecko_CalcStyleDifference.

components/layout/animation.rs

@@ -161,7 +161,9 @@ pub fn recalc_style_for_animations(context: &LayoutContext,
                                            &mut fragment.style,
                                            &ServoMetricsProvider);
                 let difference =
-                    RestyleDamage::compute_style_difference(&old_style, &fragment.style);
+                    RestyleDamage::compute_style_difference(&old_style,
+                                                            &old_style,
+                                                            &fragment.style);
                 damage |= difference.damage;
             }
         }

components/style/gecko/restyle_damage.rs

@@ -48,14 +48,14 @@ impl GeckoRestyleDamage {
     /// accessed from layout.
     pub fn compute_style_difference(
         source: &nsStyleContext,
-        new_style: &Arc<ComputedValues>
+        old_style: &ComputedValues,
+        new_style: &Arc<ComputedValues>,
     ) -> StyleDifference {
-        // TODO(emilio): Const-ify this?
-        let context = source as *const nsStyleContext as *mut nsStyleContext;
         let mut any_style_changed: bool = false;
         let hint = unsafe {
-            bindings::Gecko_CalcStyleDifference(context,
+            bindings::Gecko_CalcStyleDifference(old_style.as_style_context(),
                                                 new_style.as_style_context(),
+                                                source.mBits,
                                                 &mut any_style_changed)
         };
         let change = if any_style_changed { StyleChange::Changed } else { StyleChange::Unchanged };

components/style/matching.rs

@@ -768,7 +768,7 @@ pub trait MatchMethods : TElement {
     ) -> StyleDifference {
         debug_assert!(pseudo.map_or(true, |p| p.is_eager()));
         if let Some(source) = self.existing_style_for_restyle_damage(old_values, pseudo) {
-            return RestyleDamage::compute_style_difference(source, new_values)
+            return RestyleDamage::compute_style_difference(source, old_values, new_values)
         }
 
         let new_display = new_values.get_box().clone_display();

components/style/servo/restyle_damage.rs

@@ -60,7 +60,8 @@ impl HeapSizeOf for ServoRestyleDamage {
 impl ServoRestyleDamage {
     /// Compute the `StyleDifference` (including the appropriate restyle damage)
     /// for a given style change between `old` and `new`.
-    pub fn compute_style_difference(old: &ComputedValues,
+    pub fn compute_style_difference(_source: &ComputedValues,
+                                    old: &ComputedValues,
                                     new: &ComputedValues)
                                     -> StyleDifference {
         let damage = compute_damage(old, new);