Cleanup: Pass std::string as const reference from sync/

Cleanup: Pass std::string as const reference from sync/

Passing std::string by reference can prevent extra copying of object.

BUG=367418
TEST=
R=pavely@chromium.org,stanisc@chromium.org,zea@chromium.org

Committed: https://crrev.com/063ac230c8e9dfeb19d85afcb9d240a0008763aa
Cr-Commit-Position: refs/heads/master@{#350126}

[pavely, 2015-09-21 18:13:06]

lgtm

[ki.stfu, 2015-09-21 21:14:06]

The CQ bit was checked by ki.stfu@gmail.com

[commit-bot: I haz the power, 2015-09-21 21:14:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348313003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348313003/1

[commit-bot: I haz the power, 2015-09-21 21:31:50]

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

[commit-bot: I haz the power, 2015-09-21 21:31:51]

Try jobs failed on following builders:
  android_compile_dbg on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/android_compile...)
  linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[ki.stfu, 2015-09-21 21:43:57]

On 2015/09/21 18:13:06, pavely wrote:
> lgtm

pavely@: Please review PS2.

[ki.stfu, 2015-09-21 21:44:08]

The CQ bit was checked by ki.stfu@gmail.com to run a CQ dry run

[commit-bot: I haz the power, 2015-09-21 21:45:41]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348313003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348313003/20001

[ki.stfu, 2015-09-21 21:49:32]

The CQ bit was checked by ki.stfu@gmail.com to run a CQ dry run

[commit-bot: I haz the power, 2015-09-21 21:50:27]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348313003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348313003/40001

[commit-bot: I haz the power, 2015-09-21 22:31:36]

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

[commit-bot: I haz the power, 2015-09-21 22:31:41]

Dry run: This issue passed the CQ dry run.

[pavely, 2015-09-22 05:09:24]

lgtm

[ki.stfu, 2015-09-22 07:50:43]

The CQ bit was checked by ki.stfu@gmail.com

[commit-bot: I haz the power, 2015-09-22 07:50:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348313003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348313003/40001

[commit-bot: I haz the power, 2015-09-22 07:55:31]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-09-22 07:56:23]

Patchset 3 (id:??) landed as
https://crrev.com/063ac230c8e9dfeb19d85afcb9d240a0008763aa
Cr-Commit-Position: refs/heads/master@{#350126}