Added test checking that m-p user adding UI is visible after show.

Added test checking that m-p user adding UI is visible after show.

We have been reported that user adding UI was invisible once in M35.
I was not able to find the source of this problem, maybe it is gone
already. I wrote this test, just in case.

BUG=362153
TEST=UserAddingScreenTest.*ScreenVisibility

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271030

[Nikita (slow), 2014-05-16 12:15:40]

lgtm

[dzhioev (left Google), 2014-05-16 12:23:03]

The CQ bit was checked by dzhioev@chromium.org

[commit-bot: I haz the power, 2014-05-16 12:23:30]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dzhioev@chromium.org/290083005/1

[commit-bot: I haz the power, 2014-05-16 12:52:29]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/7...)
  android_chromium_gn_compile_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_chromium_gn_c...)
  android_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/bui...)
  android_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg/builds/18...)
  chromium_presubmit on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/chromium_presubmit/bu...)
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)
  ios_rel_device on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device/builds...)
  ios_rel_device_ninja on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device_ninja/...)
  linux_chromium_chromeos_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)
  linux_chromium_chromeos_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)
  linux_chromium_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_clang_...)
  linux_chromium_gn_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_gn_rel...)
  linux_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_rel/bu...)
  mac_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_compile_...)
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)
  win_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_compile_...)
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)
  linux_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu/builds/...)

[dzhioev (left Google), 2014-05-16 12:54:42]

The CQ bit was checked by dzhioev@chromium.org

[commit-bot: I haz the power, 2014-05-16 12:54:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dzhioev@chromium.org/290083005/20001

[commit-bot: I haz the power, 2014-05-16 16:25:07]

Change committed as 271030