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

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

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

BUG=367418
TEST=
R=dalecurtis@chromium.org,jrummell@chromium.org,sandersd@chromium.org

Committed: https://crrev.com/7cc8a91e606147efa653b1d85743052296af757f
Cr-Commit-Position: refs/heads/master@{#350046}

[DaleCurtis, 2015-09-21 16:13:03]

lgtm

[ki.stfu, 2015-09-21 17:17:10]

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

[commit-bot: I haz the power, 2015-09-21 17:17:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1360523002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1360523002/1

[commit-bot: I haz the power, 2015-09-21 18:30:13]

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

[commit-bot: I haz the power, 2015-09-21 18:30:13]

Try jobs failed on following builders:
  win8_chromium_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_ng/...)

[ki.stfu, 2015-09-21 21:20:03]

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 21:22:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1360523002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1360523002/1

[commit-bot: I haz the power, 2015-09-21 21:43:37]

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

[commit-bot: I haz the power, 2015-09-21 21:43:38]

Dry run: This issue passed the CQ dry run.

[ki.stfu, 2015-09-21 22:10:31]

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

[commit-bot: I haz the power, 2015-09-21 22:12:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1360523002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1360523002/1

[commit-bot: I haz the power, 2015-09-21 22:21:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-21 22:22:54]

Patchset 1 (id:??) landed as
https://crrev.com/7cc8a91e606147efa653b1d85743052296af757f
Cr-Commit-Position: refs/heads/master@{#350046}