This addresses cases where image elements end up making multiple requests, as well as makes the element respond to additional relevant mutations that trigger updating the image data. --- - [X] `./mach build -d` does not report any errors - [X] `./mach test-tidy` does not report any errors - [X] These changes fix #15709 (github issue number if applicable). - [X] There are tests for these changes Source-Repo: https://github.com/servo/servo Source-Revision: f90fc2fa885fd63901c4a14ee70b0169c10efbd0