If the provided ID is smaller than the corner clipping vector, we would
shrink the vector to match. This causes a crash when we have nested
PaintContext instances (as these IDs are allocated by PaintContext),
each of which perform radius painting.
This is seen on https://www.strava.com/login when it loads a reCAPTCHA.
The outer div has a border radius, which contains the reCAPTCHA in an
iframe. That iframe contains an SVG which also has a border radius.
We currently have a handful of iframe tests whose sources are in the
"input" directory. This means they get run as their own tests, when they
are really just helper files. We've had to add empty test expectation
files for these "tests", and invoke a dummy test() method just to keep
the test runner happy.
Instead, move them to their own directory so the test runner does not
see them at all.
