Instead of generating a frame for every display list, which might be one
rendered frame per `<iframe>`, generate only a single frame per call to
"update the rendering." This should make rendering more efficient when
there are `<iframe>`s present and also open up optimizations for
non-display list frames.
Testing: This could potentially reduce flashing of content during
rendering
updates, but that is very difficult to test.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
e7a963cca0