cc: Properly detect when child Surfaces idle

cc: Properly detect when child Surfaces idle

all_active_child_surfaces_ready_to_draw_ was not updated properly,
which can cause the deadline to run later than necessary when
only the root surface consistently has damage, such as during a
Browser animation.

BUG=492035
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/60bbd25b7306994330adfcee8b4689da266280a0
Cr-Commit-Position: refs/heads/master@{#331887}

[brianderson, 2015-05-28 02:02:19]

brianderson@chromium.org changed reviewers:
+ jbauman@chromium.org, mithro@mithis.com, sunnyps@chromium.org

[brianderson, 2015-05-28 02:02:19]

ptal

[jbauman, 2015-05-28 21:58:45]

lgtm

[brianderson, 2015-05-28 22:03:02]

The CQ bit was checked by brianderson@chromium.org

[commit-bot: I haz the power, 2015-05-28 22:03:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1155183004/1

[commit-bot: I haz the power, 2015-05-28 23:55:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-28 23:57:22]

Patchset 1 (id:??) landed as
https://crrev.com/60bbd25b7306994330adfcee8b4689da266280a0
Cr-Commit-Position: refs/heads/master@{#331887}