Make panels have their own shelf item in Unity

Make panels have their own shelf item in Unity.

This has the side effect of MOSTLY resolving the issue of panels always
getting focus when Chrome is activated via Alt+Tab irrespective of which
Chrome window was last activate.
- Docked "Hangouts" panels will no longer steal focus when the Chrome/browser
shelf item is activated via Alt+Tab
- Docked "Hangouts" panels will steal focus when the "Hangouts" shelf item is
activated via Alt+Tab. In particular, if there is a docked "Hangouts" panel,
the docked panel will be activated by Alt+Tab even if there is a
detached "Hangouts" panel which was more recently active.

BUG=371621
TEST=Manual, see bug

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=278804

[pkotwicz, 2014-06-19 03:57:39]

Elliot, can you please take a look before I send the CL off to a panel OWNER?

This CL mirrors what we do on Windows with ui::win::SetAppIdForWindow()
In the GTK port we resolved the bug by setting _NET_WM_STATE_SKIP_TASKBAR on
panel windows when they were docked.

[Elliot Glaysher, 2014-06-19 17:26:46]

lgtm

[pkotwicz, 2014-06-19 19:56:57]

jianli@ for OWNERS

[jianli, 2014-06-19 22:01:16]

lgtm

[pkotwicz, 2014-06-19 22:03:49]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-19 22:04:56]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/333593003/20001

[commit-bot: I haz the power, 2014-06-20 03:06:58]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/8...)
  android_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/bui...)
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)

[commit-bot: I haz the power, 2014-06-20 03:17:37]

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

[commit-bot: I haz the power, 2014-06-20 03:17:38]

Try jobs failed on following builders:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/8...)

[pkotwicz, 2014-06-20 14:17:07]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-20 14:18:49]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/333593003/20001

[commit-bot: I haz the power, 2014-06-20 14:21:21]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/8...)

[commit-bot: I haz the power, 2014-06-20 14:28:54]

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

[commit-bot: I haz the power, 2014-06-20 14:28:55]

Try jobs failed on following builders:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/8...)

[pkotwicz, 2014-06-20 18:51:03]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-20 19:03:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/333593003/20001

[commit-bot: I haz the power, 2014-06-20 19:54:29]

Change committed as 278804