Re: [css-display]? Compositing, expensive things, and laziness

Here's some pictures of the example in my previous post.

This is right now:

 +--------------------+
 |xxxxxxxx            |
 |        x           |
 |         x          |
 |          x         |
 |           x        |
 |            xxxxxxxx|
 +--------------------+
 |            xxxxxxxx|
 |           x        |
 |          x         |
 |         x          |
 |        x           |
 |xxxxxxxx            |
 +--------------------+

The graph starts at the time the .ready class is added, and charts the
progress of the opacity animations.  The first line is for the spinner, the
second is for the expensive-to-paint item.  Because transitions have to
move in lockstep, but we're not immediately ready to start painting the
expensive item, we delay both transitions until everything's ready.

We'd like to let authors annotate their page such that you get this graph
instead:

 +--------------------+
 |x                   |
 | x                  |
 |  x                 |
 |   x                |
 |    x               |
 |     xxxxxxxxxxxxxxx|
 +--------------------+
 |            xxxxxxxx|
 |           x        |
 |          x         |
 |         x          |
 |        x           |
 |xxxxxxxx            |
 +--------------------+

Where the spinner goes ahead and starts its transition immediately, without
waiting for the expensive item to be ready.

~TJ