Mac: Partially enable partial swap

Mac: Partially enable partial swap

We draw all contents in the IOSurface and remote CALayer paths into a
buffer, which we then draw to the screen. A partial swap here means that
we partially re-drew the buffer.

This isn't a complete partial swap, because, in both of these cases, we
still re-draw the full buffer to the screen.

While I'm in the neighborhood, clean up how we track the size of the
frame, since that is particularly confusing (especially when we have
partial swaps that would, more logically, pass in the damage rect).

BUG=474299
Committed: https://crrev.com/c85aba5fa461901d8b76c4fe26719ec6056abd20
Cr-Commit-Position: refs/heads/master@{#324658}

[ccameron, 2015-04-08 00:26:56]

ccameron@chromium.org changed reviewers:
+ jbauman@chromium.org

[jbauman, 2015-04-08 00:40:31]

lgtm, though this is semantically more of a preserve than a partial swap.
Luckily the compositor always seems to scissor out portions that it doesn't
intend to swap, so this works.

[ccameron, 2015-04-10 16:48:18]

Thanks!

[ccameron, 2015-04-10 16:48:22]

The CQ bit was checked by ccameron@chromium.org

[commit-bot: I haz the power, 2015-04-10 16:48:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1065123002/1

[commit-bot: I haz the power, 2015-04-10 17:44:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-10 17:45:09]

Patchset 1 (id:??) landed as
https://crrev.com/c85aba5fa461901d8b76c4fe26719ec6056abd20
Cr-Commit-Position: refs/heads/master@{#324658}