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`.
The if statement in the dispatch implies we are in the idle state, so of
course the active time will always be undefined. If this was cancelled
via a call to cancel(), we can save the time at that point. Otherwise,
just send 0.
