[Editing][CodeHealth] remove default argument 'host' in EditingTestBase::setShadowContent

[Editing][CodeHealth] remove default argument 'host' in 
EditingTestBase::setShadowContent

It is hard to understand setShadowContent puts content to a 'host' ID element.
Let's call explicitly.

BUG=
TEST=<no behavior changes>

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201460

[yoichio, 2015-08-28 06:34:59]

yoichio@chromium.org changed reviewers:
+ yosin@chromium.org

[yosin_UTC9, 2015-08-28 06:46:59]

lgtm

I guess original code has hard coded "host".

[yoichio, 2015-08-28 07:07:15]

The CQ bit was checked by yoichio@chromium.org

[commit-bot: I haz the power, 2015-08-28 07:07:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1304363008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1304363008/1

[yoichio, 2015-08-28 07:08:16]

The CQ bit was unchecked by yoichio@chromium.org

[yoichio, 2015-08-28 07:08:28]

The CQ bit was checked by yoichio@chromium.org

[commit-bot: I haz the power, 2015-08-28 07:08:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1304363008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1304363008/1

[commit-bot: I haz the power, 2015-08-28 08:26:05]

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

[commit-bot: I haz the power, 2015-08-28 08:26:06]

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

[yoichio, 2015-08-31 02:02:08]

The CQ bit was checked by yoichio@chromium.org

[yoichio, 2015-08-31 02:02:08]

The patchset sent to the CQ was uploaded after l-g-t-m from yosin@chromium.org
Link to the patchset: https://codereview.chromium.org/1304363008/#ps20001
(title: "Rebase")

[commit-bot: I haz the power, 2015-08-31 02:02:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1304363008/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1304363008/20001

[commit-bot: I haz the power, 2015-08-31 02:50:40]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201460