Perform deep copy of NavigationItems for serialization.

Perform deep copy of NavigationItems for serialization.

This fixes the race condition in which NavigationItems that were
constructed on the main thread are being deallocated on the IO thread
during session serialization.

BUG=none

Committed: https://crrev.com/73915e9ce18847fb5ab8672ed01b0af2057f8890
Cr-Commit-Position: refs/heads/master@{#344059}

[kkhorimoto, 2015-08-18 21:06:56]

kkhorimoto@chromium.org changed reviewers:
+ bhnascar@chromium.org, eugenebut@chromium.org

[kkhorimoto, 2015-08-18 21:06:57]

This prevents hitting the thread checker DCHECK when NavigationItems are
deallocated on the IO thread.

[Eugene But (OOO till 7-30), 2015-08-18 21:26:25]

lgtm, thanks for fixing this

[bhnascar, 2015-08-18 21:29:18]

On 2015/08/18 21:26:25, eugenebut wrote:
> lgtm, thanks for fixing this

LGTM, thanks!

[kkhorimoto, 2015-08-18 21:33:06]

The CQ bit was checked by kkhorimoto@chromium.org

[commit-bot: I haz the power, 2015-08-18 21:34:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292143004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292143004/1

[commit-bot: I haz the power, 2015-08-18 22:48:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-18 22:49:16]

Patchset 1 (id:??) landed as
https://crrev.com/73915e9ce18847fb5ab8672ed01b0af2057f8890
Cr-Commit-Position: refs/heads/master@{#344059}