The WPT tests require the shortest possible serialization that support
an 8 bits roundtrip.
As an example, `128` is serialized to `0.5` while `127` needs more
precision and thus will be serialized to `0.498`.
This commit fixes 33 WPT subtests in css/css-color.
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`.
This obviously excludes all shorthand properties. Eventually this test
should contain a property entry for all CSS value and animation types
(lengths, colors, custom animated properties, etc).
