This CL sets it so that the actual object size is reported only when
cppgc_enable_object_names is set to true. Otherwise the heap snapshot
merges nodes and the sizes don't make sense.

Also, this will resolve a web test failure for the library.

Bug: chromium:1056170
Change-Id: I32f6552560bdfad4b64c67b21292543978042a81
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2726499Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73092}