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`.
It does fetching and uses parseFromString() DOMParser API in the fetch
callback. Following steps end up hanging before reverting
664611bae4:
1. Do fetching initiated by fetch() js call.
2. Invoke fetch callback on networking task source
3. Fetch callback does parseFromString()
4. parseFromString() invokes HTMLParser
5. HTMLLinkElement inserted into new document initiates fetching
6. Fetching callback cannot run because networking source was blocked on
step 2.
7. HTMLParser::the_end() spins waiting for HTMLLinkElement to unblock
load event, which will never happen because fetching callback cannot
proceed.
