This allows us to disable test output, which performs expensive assert
tracking. This was making our imported tests run significantly slower
than tests run via `WPT.sh`.
Formatting the output ourselves also allows us to remove unnecessary
information from the test output.
This commit also rebaselines all existing imported WPT tests to follow
the new format.
Size negotiation should not occur for other viewports, such as iframe,
since that would allow content inside the iframe to affect the size of
the iframe in the containing document.
300 new subtest passes on WPT. :^)
In the case where we had a preferred aspect ratio and a natural height
but no natural width, we'd get into ping-ponging infinite recursion by
trying to find the width to resolve the height to resolve the width to
resolve the height...
