Sync: ChangeReorderBuffer::Traversal should handle nodes with unset Parent ID

Sync: ChangeReorderBuffer::Traversal should handle nodes with unset Parent ID

When reording sync nodes for an update, treat sync nodes with implicit
parent folder as if they were linked directly under the directory root.
That is safe to do because only non-hierarchical datatype nodes might
have unset parent IDs and those nodes are OK to handle in any order.

BUG=438313
Committed: https://crrev.com/7c880b539f7ea8e13cbe6930b01fe38a1aad78b0
Cr-Commit-Position: refs/heads/master@{#320145}

[stanisc, 2015-03-10 22:53:23]

Patchset #1 (id:1) has been deleted

[stanisc, 2015-03-11 01:37:07]

stanisc@chromium.org changed reviewers:
+ pavely@chromium.org

[stanisc, 2015-03-11 01:37:07]

Please take a look.
This is one missing case for handling updates for nodes with implicit (unset)
parent IDs.

[pavely, 2015-03-11 17:42:37]

lgtm

[stanisc, 2015-03-11 20:34:17]

The CQ bit was checked by stanisc@chromium.org

[commit-bot: I haz the power, 2015-03-11 20:35:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/993153002/20001

[commit-bot: I haz the power, 2015-03-11 21:03:36]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-03-11 21:04:21]

Patchset 1 (id:??) landed as
https://crrev.com/7c880b539f7ea8e13cbe6930b01fe38a1aad78b0
Cr-Commit-Position: refs/heads/master@{#320145}