Revert of Wallpaper manager now observing user child user status to update...

Revert of Wallpaper manager now observing user child user status to update default wallpaper. (patchset #2 id:20001 of https://codereview.chromium.org/952853002/)

Reason for revert:
MultiUserNotificationBlockerChromeOSTest is failing after this CL (see issue 463049).

Original issue's description:
> Wallpaper manager now observing user child user status to update default wallpaper.
>
> BUG=461282
>
> Committed: https://crrev.com/c3a3f671f8e0c5777c6bc825f21d61c6bcafbec3
> Cr-Commit-Position: refs/heads/master@{#318666}

TBR=bshe@chromium.org,skuhne@chromium.org,merkulova@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=461282

Review URL: https://codereview.chromium.org/966333004

Cr-Commit-Position: refs/heads/master@{#318669}

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc

@@ -307,8 +307,6 @@ WallpaperManager::WallpaperManager()
           base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
   wallpaper_loader_ = new UserImageLoader(ImageDecoder::ROBUST_JPEG_CODEC,
                                           task_runner_);
-
-  user_manager::UserManager::Get()->AddSessionStateObserver(this);
 }
 
 WallpaperManager::~WallpaperManager() {
@@ -316,8 +314,6 @@ WallpaperManager::~WallpaperManager() {
   // http://crbug.com/171694
   DCHECK(!show_user_name_on_signin_subscription_);
 
-  user_manager::UserManager::Get()->RemoveSessionStateObserver(this);
-
   ClearObsoleteWallpaperPrefs();
   weak_factory_.InvalidateWeakPtrs();
 }
@@ -970,10 +966,6 @@ size_t WallpaperManager::GetPendingListSizeForTesting() const {
   return loading_.size();
 }
 
-void WallpaperManager::UserChangedChildStatus(user_manager::User* user) {
-  SetUserWallpaperNow(user->email());
-}
-
 void WallpaperManager::OnDefaultWallpaperDecoded(
     const base::FilePath& path,
     const wallpaper::WallpaperLayout layout,

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h

@@ -21,7 +21,6 @@
 #include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "components/user_manager/user.h"
 #include "components/user_manager/user_image/user_image.h"
-#include "components/user_manager/user_manager.h"
 #include "components/wallpaper/wallpaper_layout.h"
 #include "components/wallpaper/wallpaper_manager_base.h"
 #include "content/public/browser/notification_observer.h"
@@ -31,9 +30,7 @@
 
 namespace chromeos {
 
-class WallpaperManager :
-    public wallpaper::WallpaperManagerBase,
-    public user_manager::UserManager::UserSessionStateObserver {
+class WallpaperManager : public wallpaper::WallpaperManagerBase {
  public:
   class PendingWallpaper;
 
@@ -118,9 +115,6 @@ class WallpaperManager :
   // Returns queue size.
   size_t GetPendingListSizeForTesting() const override;
 
-  // Overridden from user_manager::UserManager::UserSessionStateObserver:
-  void UserChangedChildStatus(user_manager::User* user) override;
-
  private:
   friend class TestApi;
   friend class WallpaperManagerBrowserTest;

chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos_unittest.cc

@@ -18,12 +18,10 @@
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
-#include "chrome/browser/chromeos/login/users/scoped_user_manager_enabler.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos.h"
 #include "chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.h"
 #include "chrome/test/base/testing_profile.h"
-#include "components/user_manager/fake_user_manager.h"
 #include "components/user_manager/user_info.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window_event_dispatcher.h"
@@ -41,9 +39,7 @@ class MultiUserWindowManagerChromeOSTest : public AshTestBase {
  public:
   MultiUserWindowManagerChromeOSTest()
       : multi_user_window_manager_(NULL),
-        session_state_delegate_(NULL),
-        fake_user_manager_(new user_manager::FakeUserManager),
-        user_manager_enabler_(fake_user_manager_) {}
+        session_state_delegate_(NULL) {}
 
   void SetUp() override;
   void TearDown() override;
@@ -162,10 +158,6 @@ class MultiUserWindowManagerChromeOSTest : public AshTestBase {
   // The session state delegate.
   ash::test::TestSessionStateDelegate* session_state_delegate_;
 
-  user_manager::FakeUserManager* fake_user_manager_;  // Not owned.
-
-  chromeos::ScopedUserManagerEnabler user_manager_enabler_;
-
   // The maximized window manager (if enabled).
   scoped_ptr<MaximizeModeWindowManager> maximize_mode_window_manager_;