Break points are cleared to empty fixed array, not undefined.

R=jgruber@chromium.org

Change-Id: Id8dcd08ed0aebc5c4f7745982cde48d562af9772
Reviewed-on: https://chromium-review.googlesource.com/904202Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51117}