Moves maintaining ShellObservers back to Shell

ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc

Index: ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc
diff --git a/ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc b/ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc
index d845f67201d4cb606b5688bf4cbba7c18a918e9f..daa53f7f4c38c89430c17365b828269e2998f9b1 100644
--- a/ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc
+++ b/ash/common/system/chromeos/screen_security/screen_capture_tray_item.cc
@@ -11,6 +11,7 @@
 #include "ash/common/system/tray/system_tray_notifier.h"
 #include "ash/common/wm_shell.h"
 #include "ash/resources/grit/ash_resources.h"
+#include "ash/shell.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -28,12 +29,12 @@ const char kScreenCaptureNotificationId[] = "chrome://screen/capture";
 
 ScreenCaptureTrayItem::ScreenCaptureTrayItem(SystemTray* system_tray)
     : ScreenTrayItem(system_tray, UMA_SCREEN_CAPTURE) {
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
   WmShell::Get()->system_tray_notifier()->AddScreenCaptureObserver(this);
 }
 
 ScreenCaptureTrayItem::~ScreenCaptureTrayItem() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   WmShell::Get()->system_tray_notifier()->RemoveScreenCaptureObserver(this);
 }