[Resource-Timing] Fixup nested object tests. Add an extra check.

The nested object test was failing as the object element wasn't being
reloaded when the main page navigated back. That only happens when the
type of the object is not defined.

This CL fixes the test by adding a type to the object. In the debugging
process I also noticed that we don't verify that the entry is not exposed
before navigating back, so added an extra check to that effect.

Bug: 941482
Change-Id: Ia2ba73e885c20653f582f3a84226abc564f97ed5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1581199
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653695}
5 files changed