Auto merge of #17802 - emilio:reland-stuff, r=heycam

Revert "Backed out changeset b10e6ba9cbdb because gecko part had to b…

…e backed out."

This reverts commit b96d96d448.

The fix on the Gecko side is trivial, and I can land it after this lands.

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components/style/gecko/generated/bindings.rs

@@ -1047,8 +1047,9 @@ extern "C" {
      -> CSSPseudoElementType;
 }
 extern "C" {
-    pub fn Gecko_CalcStyleDifference(oldstyle: *mut nsStyleContext,
-                                     newstyle: ServoComputedValuesBorrowed,
+    pub fn Gecko_CalcStyleDifference(old_style: *const ServoStyleContext,
+                                     new_style: *const ServoStyleContext,
+                                     old_style_bits: u64,
                                      any_style_changed: *mut bool)
      -> nsChangeHint;
 }

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,
-                                                &new_style,
+            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 };