Types such as "function" have a ValueMirror that does not override
"buildObjectPreview()". This CL updates clients to check that the
preview was actually built after call it.

Bug: chromium:907400
Change-Id: Id569c98363d47b259a40790b596efedb3d14abc2
Reviewed-on: https://chromium-review.googlesource.com/c/1347067Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57703}