[Sync] Give custom themes priority over default themes

[Sync] Give custom themes priority over default themes at signin time

Previously a default theme could overwrite a custom theme if the default
was already synced. Now, when a user signs in to sync on a new device,
custom themes will have priority.

BUG=440232
Committed: https://crrev.com/bee53729a8f430e4a8c92ec8a5bfc82952b50a27
Cr-Commit-Position: refs/heads/master@{#338398}

[Nicolas Zea, 2015-07-10 00:40:58]

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

[Nicolas Zea, 2015-07-10 00:40:58]

PTAL

[pavely, 2015-07-10 17:51:20]

lgtm

[Nicolas Zea, 2015-07-10 18:07:30]

The CQ bit was checked by zea@chromium.org

[commit-bot: I haz the power, 2015-07-10 18:08:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1229953004/1

[commit-bot: I haz the power, 2015-07-10 18:18:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-07-10 18:18:11]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[Nicolas Zea, 2015-07-10 22:27:06]

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

[Nicolas Zea, 2015-07-10 22:27:06]

+Peter for owners

[pkotwicz, 2015-07-10 23:35:42]

LGTM

Can you please specify in the CL description what effect this CL has? My
understanding is that this CL only affects the behavior when the user logs into
sync.

[Nicolas Zea, 2015-07-10 23:44:12]

On 2015/07/10 23:35:42, pkotwicz wrote:
> LGTM
> 
> Can you please specify in the CL description what effect this CL has? My
> understanding is that this CL only affects the behavior when the user logs
into
> sync.

Correct. Updated message.

[Nicolas Zea, 2015-07-10 23:44:18]

The CQ bit was checked by zea@chromium.org

[commit-bot: I haz the power, 2015-07-10 23:44:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1229953004/1

[commit-bot: I haz the power, 2015-07-10 23:50:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-10 23:51:55]

Patchset 1 (id:??) landed as
https://crrev.com/bee53729a8f430e4a8c92ec8a5bfc82952b50a27
Cr-Commit-Position: refs/heads/master@{#338398}