Resizes in inactive pipelines probably don't trigger responsive image updates when the pipeline becomes active

[jdm]

ScriptThread::handle_resize_inactive_msg just calls Window::set_window_size. handle_resize_event calls window.evaluate_media_queries_and_report_changes();, so we probably want to store a flag on the window that means "if I ever become active again, reevaluate media queries". It should be possible to test this with an iframe that loads page A with responsive content, then loads page B, the iframe is resized, and then we go back in session history to page A and verify that the responsive content has been affected by the resize.