[Merge-M54] arc: Show icon for the task created in background.

[Merge-M54] arc: Show icon for the task created in background.

There is support for Arc tasks which don't have window on creation
time.

TBR=reviewer@chromium.org
NOTRY=true
NOPRESUBMIT=true

BUG=b/31780038
BUG=651225
TEST=Manually on device. Various cases with deferred launch, pinned
     non-pinned apps, switch to secondary user profile and back.
     In all cases we have shelf icon for apps, even if another Arc
     app is active in full screen. In case of switching to the
     secondary profile, there is no Arc icons, including those,
     which don't have window attached.

Review-Url: https://codereview.chromium.org/2381713002
Cr-Commit-Position: refs/heads/master@{#421833}

[khmel, 2016-10-03 20:31:01]

The CQ bit was checked by khmel@chromium.org

[commit-bot: I haz the power, 2016-10-03 20:32:24]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-03 20:35:10]

Committed patchset #1 (id:1)