This CL hardens the test function for unwrapping the C++ object to
only do so if the correct API object is passed from JS.

Bug: chromium:1201057
Change-Id: I81eb16efe2711bd788c775e3bcb712720bbe4782
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843347Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74102}