Auto merge of #12373 - cynicaldevil:impl-runnable, r=KiChjang

Implements name method for FilerReader event from trait Runnable

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12334

<!-- Either: -->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12373)
<!-- Reviewable:end -->

components/script/dom/filereader.rs

@@ -380,6 +380,8 @@ pub enum FileReaderEvent {
 }
 
 impl Runnable for FileReaderEvent {
+    fn name(&self) -> &'static str { "FileReaderEvent" }
+
     fn handler(self: Box<FileReaderEvent>) {
         let file_reader_event = *self;
         match file_reader_event {