Change Observers: Add basic WPTs
Adds some WPTs that just test the basic expectations of the API.
Bug: 341136316
Change-Id: I1d21afef7f920ecf58745f8b2a628918250c6b2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5739854
Reviewed-by: Daseul Lee dslee@chromium.org
Commit-Queue: Nathan Memmott memmott@chromium.org
Cr-Commit-Position: refs/heads/main@{#1333296}