Chrome-crash tells me that occasionally a function gets stripped of an
initial map entirely (e.g. report 917de3c31d0e0d9b).

R=jarin@chromium.org

Change-Id: Ie0103695c4801a4c2cbc488af91c3d580efe4eab
Reviewed-on: https://chromium-review.googlesource.com/1143483Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54568}