Reland: Enable Wallet metadata sync.

Reland: Enable Wallet metadata sync.

Originally landed in https://crrev.com/90c4e947, which enabled a code
path where https://crrev.com/6aeb9079 introduced a bug a few hours
earlier. The bug was detected in tests, which resulted in a revert.
https://crrev.com/7a8e3fdf fixed the bug in the hidden code path. It's
safe to reland now.

TBR=zea@chromium.org, estade@chromium.org
BUG=481595
Committed: https://crrev.com/0b999094d4ce8a462b70327cc38ca117313a1504
Cr-Commit-Position: refs/heads/master@{#353927}

[please use gerrit instead, 2015-10-13 22:44:44]

The CQ bit was checked by rouslan@chromium.org

[commit-bot: I haz the power, 2015-10-13 22:48:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1396883005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1396883005/1

[commit-bot: I haz the power, 2015-10-14 00:45:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-14 00:46:42]

Patchset 1 (id:??) landed as
https://crrev.com/0b999094d4ce8a462b70327cc38ca117313a1504
Cr-Commit-Position: refs/heads/master@{#353927}

[nednguyen, 2015-11-13 21:10:49]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1444743002/ by nednguyen@google.com.

The reason for reverting is: Speculative revert to see if this patch regresses
blink_perf.shadow_dom benchmark.