prepare for 0.12.20+9 (#586)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a962fec..cba4bef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.12.20+9
+
+* Introduce new flag `--chain-stack-traces` to conditionally chain stack traces.
+
 ## 0.12.20+8
 
 * Fixed more blockers for compiling with `dev_compiler`.
diff --git a/pubspec.yaml b/pubspec.yaml
index cb75fa3..4cbd2eb 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 0.12.20+8
+version: 0.12.20+9
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test