Revert "Backed out changeset b10e6ba9cbdb because gecko part had to be backed out."

This reverts commit b96d96d448.

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

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;
 }