servo: Merge #16907 - Bug 1364862: Make PostRebuildAllStyleData async. r=heycam (from emilio:postrebuild); r=heycam

Source-Repo: https://github.com/servo/servo
Source-Revision: c2d5b0006ce45930184cb9f8edb5e0a8146512f7

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 4c2b40eec4c4e2824e69e9bfb71a82da9661cbcf

servo/ports/geckolib/glue.rs

@@ -1122,6 +1122,12 @@ pub extern "C" fn Servo_StyleSet_RebuildData(raw_data: RawServoStyleSetBorrowed)
     data.reset_device(&guard);
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_Clear(raw_data: RawServoStyleSetBorrowed) {
+    let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
+    data.clear_stylist();
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_StyleSet_Drop(data: RawServoStyleSetOwned) {
     let _ = data.into_box::<PerDocumentStyleData>();