Fix crash in NativeMessageProcessHost

Fix crash in NativeMessageProcessHost

We should initialize the |client_| pointer before launching the host process,
as the OnHostProcessLaunched() callback dereferences the |client_| pointer.

BUG=421500
Committed: https://crrev.com/d19b0657cafb67b266c45bac36bc4ba87a04596a
Cr-Commit-Position: refs/heads/master@{#299030}

[kelvinp, 2014-10-09 22:36:56]

kelvinp@chromium.org changed reviewers:
+ kalman@chromium.org

[kelvinp, 2014-10-09 22:37:21]

kelvinp@chromium.org changed reviewers:
+ mpcomplete@google.com

[kelvinp, 2014-10-09 22:38:18]

PTAL

[kelvinp, 2014-10-09 22:39:09]

kelvinp@chromium.org changed reviewers:
+ mpcomplete@chromium.org
- mpcomplete@google.com

[Matt Perry, 2014-10-09 22:40:18]

lgtm

[kelvinp, 2014-10-09 22:51:28]

The CQ bit was checked by kelvinp@chromium.org

[commit-bot: I haz the power, 2014-10-09 22:53:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/642163002/1

[kelvinp, 2014-10-10 00:29:25]

The CQ bit was unchecked by kelvinp@chromium.org

[kelvinp, 2014-10-10 00:31:08]

The CQ bit was checked by kelvinp@chromium.org

[commit-bot: I haz the power, 2014-10-10 00:32:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/642163002/1

[commit-bot: I haz the power, 2014-10-10 01:08:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-10 02:04:45]

Patchset 1 (id:??) landed as
https://crrev.com/d19b0657cafb67b266c45bac36bc4ba87a04596a
Cr-Commit-Position: refs/heads/master@{#299030}