[vm/sendandexit] Add CHANGELOG for Isolate.exit([port, message]) change.

This is follow-up to 56403a0d356a3508b043f13e7f7168df3003d529.

Change-Id: I222c04fd4d41e272eeb3e8fd62c55035eee1c12c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/215143
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e61db67..e467d97 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -944,6 +944,9 @@
 - Add `debugName` positional parameter to `ReceivePort` and `RawReceivePort`
   constructors, a name which can be associated with the port and displayed in
   tooling.
+- Introduce `Isolate.exit([port, message])` which terminates current isolate
+  and, if `port` is specified, as a last action sends out the `message` out to
+  that `port`.
 
 #### `dart:html`