[release] Add release notes for 2.8.4 to the changelog

Change-Id: I5f9c36c92c17d57214eb8e5388ac46c9e10d6cef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149598
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15d525e..dc5035a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+## 2.8.4 - 2020-06-04
+
+This is a patch release that fixes potential memory leaks in the Dart front-end
+(issues [#42111][] and [#42112][]).
+
+[#42111]: https://github.com/dart-lang/sdk/issues/42111
+[#42112]: https://github.com/dart-lang/sdk/issues/42112
+
 ## 2.8.3 - 2020-05-28
 
 This is a patch release that fixes the following issues: