win: Move HWNDMessageHandler's WeakPtrFactory member to the end.

win: Move HWNDMessageHandler's WeakPtrFactory member to the end.

Fixes some

  [chromium-style] WeakPtrFactory members which refer to their outer class must
  be the last member in the outer class definition.

warnings and also makes the code more correct.

BUG=303818, 467287
Committed: https://crrev.com/b59e330a7bd6b58bfdfa31690f45aa4485b95e86
Cr-Commit-Position: refs/heads/master@{#327374}

[Nico, 2015-04-28 20:00:47]

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

[sky, 2015-04-28 20:52:50]

LGTM

[Nico, 2015-04-28 20:55:46]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-04-28 20:56:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1107353003/1

[commit-bot: I haz the power, 2015-04-28 22:08:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-28 22:10:05]

Patchset 1 (id:??) landed as
https://crrev.com/b59e330a7bd6b58bfdfa31690f45aa4485b95e86
Cr-Commit-Position: refs/heads/master@{#327374}