The `pending reflow` concept isn't necessary now that *update the
rendering* is taking care of triggering reflows at the correct time.
`Window::reflow` already avoids reflows if the page is not dirty, so
pending reflows is now just an extraneous check as long as *update the
rendering* runs properly.
This change also removes some explicit reflows, which now wait until the
appropriate moment during *update the rendering*. This should remove
some extra reflows that are not necessary.
Servo needs some way to track that resizing the web view needs to
re-layout due to the initial containing block changing. Move handling
of `Document::needs_paint` to the script thread and use this, expanding
the rustdoc to explain what it is for a bit more clearly.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
3f85a27097