Fix arm64 gc stress issue.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/306483002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21506 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/mjsunit/regress/debug-prepare-step-in.js

@@ -52,3 +52,5 @@ function g() {
 }
 
 g();
+
+Debug.setListener(null);