This change simply allows `GenerateFrame` to carry a list of
`WebViewId`s and modifies `update_the_rendering` to collect `WebViewId`s
and pass them in the `GenerateFrame` message. The list of `WebViewId`s
is currently not used and that will be handled in a follow-up patch.
Testing: Covered by existing tests.
Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>