Fix crash in deprecated Socket API.

This looks like a clear case of "use-after-delete": Given DNS resolution
can take some time to complete, the re-use of a raw pointer stored as
member variable (Socket*) is likely to be the root cause of this crash.

This can happen is a socket is destroyed in between a call to "connect"
(or "send") and the DNS resolution callback is invoked.

Both the SocketConnectFunction and SocketSendFunction used to keep
a raw pointer to the Socket instance. A call to "destroy" at the
"right" time would free the socket instance, leaving both function
to access a released object.

The fix in this CL is to re-aquire the Socket instance using a
socket_id instead of re-using the Socket* instance. If the socket
has been destroyed, the socket_id is invalid, and the function fails
gracefully.

BUG=416741
Committed: https://crrev.com/d30fe32c54da4c5da9b50d91423d6e332b5c989d
Cr-Commit-Position: refs/heads/master@{#297076}

[rpaquay, 2014-09-26 23:02:37]

rpaquay@chromium.org changed reviewers:
+ rockot@chromium.org

[Ken Rockot(use gerrit already), 2014-09-26 23:04:30]

Ah, pretty straightforward. LGTM

[rpaquay, 2014-09-26 23:06:11]

The CQ bit was checked by rpaquay@chromium.org

[commit-bot: I haz the power, 2014-09-26 23:06:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/608083002/1

[commit-bot: I haz the power, 2014-09-26 23:55:59]

Committed patchset #1 (id:1) as 691213ebccf7d8983e844b8751a82668e5c0b6c9

[commit-bot: I haz the power, 2014-09-26 23:56:36]

Patchset 1 (id:??) landed as
https://crrev.com/d30fe32c54da4c5da9b50d91423d6e332b5c989d
Cr-Commit-Position: refs/heads/master@{#297076}