We might have empty frame_inspector_ here, let's fast return in this
case.

R=yangguo@chromium.org

Bug: chromium:864920
Change-Id: Ia8012251877bb4e04b7f756db72a3039bca6fa9c
Reviewed-on: https://chromium-review.googlesource.com/1250408Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56278}