IPC: Add more debug info.

IPC: Add more debug info.

We're still seeing crashes that appear to come from multiple simultaneous
writes. Given that writing_ is false when we crash, but the operation
matches the current thread, file handle and IPC Channel, it could
be that for some reason a failed Write is still genarating a notification.

So this CL stores two error codes (one for the current operation and another
for a previous failure), and the write size.

BUG=387876
R=cpu@chromium.org

Committed: https://crrev.com/431ce7382e8cae58d1dfbdde7c5c8bdc27daee2b
Cr-Commit-Position: refs/heads/master@{#294993}

[cpu_(ooo_6.6-7.5), 2014-09-16 00:04:39]

lgtm

[cpu_(ooo_6.6-7.5), 2014-09-16 00:04:42]

The CQ bit was checked by cpu@chromium.org

[commit-bot: I haz the power, 2014-09-16 00:37:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/564863003/1

[commit-bot: I haz the power, 2014-09-16 02:45:29]

Committed patchset #1 (id:1) as 0a01cd55dcfadfa196c8ba6f3ab641aaa7e4b2d6

[commit-bot: I haz the power, 2014-09-16 02:48:03]

Patchset 1 (id:??) landed as
https://crrev.com/431ce7382e8cae58d1dfbdde7c5c8bdc27daee2b
Cr-Commit-Position: refs/heads/master@{#294993}