extensions: Improve error messages for stub windows and tabs APIs

This way an API test that uses chrome.tabs will throw an error saying
"chrome.tabs not implemented" instead of just "Not implemented".
Ditto for chrome.windows.

Bug: none
Change-Id: I4f010f29a41d12bee5a63ad3b587a82faf33afa0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6603598
Commit-Queue: James Cook <jamescook@chromium.org>
Auto-Submit: James Cook <jamescook@chromium.org>
Commit-Queue: Michael Wojcicka <mwoj@google.com>
Reviewed-by: Michael Wojcicka <mwoj@google.com>
Cr-Commit-Position: refs/heads/main@{#1467098}