Fix crash in ChromeExtensionMessageFilter::OnPostMessage

Fix crash in ChromeExtensionMessageFilter::OnPostMessage

Speculative fix: ChromeExtensionMessageFilter can outlive its Profile, so
check |profile_| for NULL in OnPostMessage as is done in other message
handlers.

BUG=419047
TEST=none

Committed: https://crrev.com/a3e007d47ef0ca2d089510a64f4760a0f8bfeadd
Cr-Commit-Position: refs/heads/master@{#297531}

[James Cook, 2014-09-30 20:34:09]

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

[James Cook, 2014-09-30 20:34:09]

rockot, since kalman is out, can you take a look?

[Ken Rockot(use gerrit already), 2014-09-30 20:38:19]

Seems right to me. Thanks and lgtm

[James Cook, 2014-09-30 20:46:16]

The CQ bit was checked by jamescook@chromium.org

[James Cook, 2014-09-30 20:46:18]

The CQ bit was unchecked by jamescook@chromium.org

[James Cook, 2014-09-30 20:48:18]

jamescook@chromium.org changed reviewers:
+ sky@chromium.org

[James Cook, 2014-09-30 20:48:19]

sky, can I get OWNERS?

If looks good without nits feel free to CQ.

[sky, 2014-09-30 21:44:12]

LGTM

[James Cook, 2014-09-30 22:12:40]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2014-09-30 22:14:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/617053002/1

[commit-bot: I haz the power, 2014-09-30 22:37:26]

Committed patchset #1 (id:1) as 9b02d5fadb92b8f8c76f6e002809b1b2806b365a

[commit-bot: I haz the power, 2014-09-30 22:38:01]

Patchset 1 (id:??) landed as
https://crrev.com/a3e007d47ef0ca2d089510a64f4760a0f8bfeadd
Cr-Commit-Position: refs/heads/master@{#297531}