DevTools: add test to verify matched styles for :host selector

DevTools: add test to verify matched styles for :host selector

This patch adds test based on the regression issue with styles sidebar
pane not showing styles for :host selectors. This test was originally
added in r174963, but the commit got reverted.

BUG=363468
TBR=apavlov

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175553

[lushnikov, 2014-06-04 14:38:34]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2014-06-04 14:39:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lushnikov@chromium.org/317703002/1

[commit-bot: I haz the power, 2014-06-04 16:25:33]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/10636)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/12845)

[commit-bot: I haz the power, 2014-06-04 17:31:06]

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

[commit-bot: I haz the power, 2014-06-04 17:31:06]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/10649)

[lushnikov, 2014-06-04 19:14:41]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2014-06-04 19:15:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lushnikov@chromium.org/317703002/1

[commit-bot: I haz the power, 2014-06-04 20:13:05]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/10667)

[commit-bot: I haz the power, 2014-06-04 21:20:44]

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

[commit-bot: I haz the power, 2014-06-04 21:20:45]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/10669)

[lushnikov, 2014-06-05 08:11:21]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2014-06-05 08:12:24]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lushnikov@chromium.org/317703002/1

[commit-bot: I haz the power, 2014-06-05 11:18:16]

Change committed as 175553