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`.
(cherry picked from commit bf668696de9a68bbcd6adfeaac809a475da015dc;
amended a bit but not as much as one might think -- see PR for details)
Rather than returning a relative URL, an absolutized URL is now
returned relative to the document base URL
(cherry picked from commit 48e5d28ec985aeaee565d06a625a0d664b6975d3)
