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`.
We had previous implemented some plumbing for file input elements in
commit 636602a54e.
This implements the return path for chromes to inform WebContent of the
file(s) the user selected. This patch includes a dummy implementation
for headless-browser to enable testing.