For example, in the following abbreviated test HTML:
<span>some text</span>
<script>println("whf")</script>
We would have to craft the expectation file to include the "some text"
segment, usually with some leading whitespace. This is a bit annoying,
and makes it difficult to manually craft expectation files.
So instead of comparing the expectation against the entire DOM inner
text, we now send the inner text of just the <pre> element containing
the test output when we invoke `internals.signalTextTestIsDone`.
While waiting for a task that populates a session history entry, we
can't limit the processing of the event loop to the
`NavigationAndTraversal` task source. This is because fetching uses the
`Networking` task source, which also needs to be processed.
Since making a fetch request might take some time, we want to process
everything on the event loop while waiting, to avoid blocking user
interactions.
It is still possible to use `spin_processing_tasks_with_source_until()`
on subsequent steps of `apply_the_history_step()`.
Also modifies test that was flaky.
In our implementation of the "apply the history step" algorithm, we
have to spin-wait for the completion of tasks queued on the event loop.
Before this change, we allowed tasks from any source to be executed
while we were waiting. It should not be possible because it allows to
interrupt history step application by anything, including another
history step application.
Fixes https://github.com/SerenityOS/serenity/issues/23598
