content: Cancel all DeletedDiscardableSharedMemory callbacks in dtor.

content: Cancel all DeletedDiscardableSharedMemory callbacks in dtor.

Avoid IPC from ChildDiscardableSharedMemoryManager dtor in case the
channel has been closed at destruction time.

BUG=467958
TEST=content_browsertests --gtest_filter=ChildDiscardableSharedMemoryManagerBrowserTest.*

Committed: https://crrev.com/3d246168a99a21215f4868de7c01b9236e28b91a
Cr-Commit-Position: refs/heads/master@{#320965}

[reveman, 2015-03-17 18:15:21]

reveman@chromium.org changed reviewers:
+ avi@chromium.org

[Avi (use Gerrit), 2015-03-17 19:58:57]

The CQ bit was checked by avi@chromium.org

[Avi (use Gerrit), 2015-03-17 19:58:57]

lgtm

[commit-bot: I haz the power, 2015-03-17 19:59:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1012163002/1

[commit-bot: I haz the power, 2015-03-17 20:46:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-17 20:46:44]

Patchset 1 (id:??) landed as
https://crrev.com/3d246168a99a21215f4868de7c01b9236e28b91a
Cr-Commit-Position: refs/heads/master@{#320965}