When an `<iframe>` cannot scroll because the size of the frame is
greater than or
equal to the size of page contents, chain up the keyboard scroll
operation to the parent frame.
Testing: A new Servo-only WPT tests is added, though needs to be
manually
run with `--product servodriver`.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Delan Azabani <dazabani@igalia.com>
Instead of having every single embedder implement keyboard scrolling,
handle it in script in the default key event handler. This allows
properly targeting the scroll events to their scroll containers as well
as appropriately sizing "page up" and "page down" scroll deltas.
This change means that when you use the keyboard to scroll, the focused
or most recently clicked `<iframe>` or overflow scroll container is
scrolled, rather than the main frame.
In addition, when a particular scroll frame is larger than its content
in the axis of the scroll, the scrolling operation is chained to
the parent (as in other browsers). One exception is for `<iframe>`s,
which will be implemented in a followup change.
Testing: automated tests runnable locally with `mach test-wpt --product
servodriver`
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
