Add FFI for debug info of CSSStyleRule

components/style/gecko_bindings/bindings.rs

@@ -1010,6 +1010,10 @@ extern "C" {
                                          index: u32)
      -> RawServoStyleRuleStrong;
 }
+extern "C" {
+    pub fn Servo_StyleRule_Debug(rule: RawServoStyleRuleBorrowed,
+                                 result: *mut nsACString_internal);
+}
 extern "C" {
     pub fn Servo_StyleRule_GetStyle(rule: RawServoStyleRuleBorrowed)
      -> RawServoDeclarationBlockStrong;

ports/geckolib/glue.rs

@@ -324,6 +324,13 @@ pub extern "C" fn Servo_StyleRule_Release(rule: RawServoStyleRuleBorrowed) -> ()
     unsafe { RwLock::<StyleRule>::release(rule) };
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_Debug(rule: RawServoStyleRuleBorrowed, result: *mut nsACString) -> () {
+    let rule = RwLock::<StyleRule>::as_arc(&rule);
+    let result = unsafe { result.as_mut().unwrap() };
+    write!(result, "{:?}", *rule.read()).unwrap();
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_GetStyle(rule: RawServoStyleRuleBorrowed) -> RawServoDeclarationBlockStrong {
     let rule = RwLock::<StyleRule>::as_arc(&rule);