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`.
In particular, there was an assertion failure due to the temporary
parser document's "about base URL" being empty when trying to "parse a
URL" during parsing.
We fix this by copying the context element's document's about base URL
to the temporary parsing document while parsing a fragment.
This fixes a crash when loading search results on https://amazon.com/
