Sync: Report unmatched unassociated node during optimistic bookmark association.

Sync Report unmatched unassociated node during optimistic bookmark association.

This will verify an assumption that all sync nodes must
be already associated and have external IDs during optimistic
association.
Running into a node with unassigned external ID would indicate
an issue with the delayed PersistAssociations task.

BUG=456876
Committed: https://crrev.com/2ef675dbcd5943aad03184b67696330cc910568d
Cr-Commit-Position: refs/heads/master@{#335998}

[stanisc, 2015-06-23 22:47:10]

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

[stanisc, 2015-06-23 22:47:11]

PTAL!

[Nicolas Zea, 2015-06-24 19:51:26]

lgtm

[stanisc, 2015-06-24 20:45:48]

The CQ bit was checked by stanisc@chromium.org

[commit-bot: I haz the power, 2015-06-24 20:47:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1207483006/1

[commit-bot: I haz the power, 2015-06-24 20:53:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-24 20:54:42]

Patchset 1 (id:??) landed as
https://crrev.com/2ef675dbcd5943aad03184b67696330cc910568d
Cr-Commit-Position: refs/heads/master@{#335998}