iCloud Passwords (Chrome Extension) Performance Bug

There is a bug in [the iCloud Passwords extension for Chrome] that causes some websites (like GitHub) to hang for 10+ seconds during navigation. A recursive DOM traversal occurs before the page is finished loading, pegging the thread at 100% and blocking page resources from loading. Once the loop finishes some resources are loaded, but the DOM change triggers the extension to restart the traversal, repeatedly blocking the page resources.

Changing `content_scripts.run_at` to "document_end" in the extension's manifest corrects the issue. I suspect `document.collectMatchingElementsInFlatTree()` is a Safari API feature that won't make it to Chrome any time soon. A proper fix might also replace the recursive loop in `content_script.js::querySelectorAllIncludingWithinShadowRoots()` with an async loop to avoid blocking the main event loop for so long.

https://chrome.google.com/webstore/detail/icloud-passwords/pejdijmoenmkgeppbflobdenhhabjlaj