Moves maintaining ShellObservers back to Shell

ash/common/system/chromeos/palette/palette_tray.cc

Index: ash/common/system/chromeos/palette/palette_tray.cc
diff --git a/ash/common/system/chromeos/palette/palette_tray.cc b/ash/common/system/chromeos/palette/palette_tray.cc
index b63ad7e5937d4a3fd8214e5c99ec2b7b26941f0f..27dfd9bc45081fcbb92dafd2e0b2c51ed3555fe9 100644
--- a/ash/common/system/chromeos/palette/palette_tray.cc
+++ b/ash/common/system/chromeos/palette/palette_tray.cc
@@ -24,6 +24,7 @@
 #include "ash/resources/grit/ash_resources.h"
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/root_window_controller.h"
+#include "ash/shell.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "base/metrics/histogram_macros.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -169,7 +170,7 @@ PaletteTray::PaletteTray(WmShelf* wm_shelf)
   tray_container()->SetMargin(kTrayIconMainAxisInset, kTrayIconCrossAxisInset);
   tray_container()->AddChildView(icon_);
 
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->AddSessionStateObserver(this);
   ui::InputDeviceManager::GetInstance()->AddObserver(this);
 }
@@ -179,7 +180,7 @@ PaletteTray::~PaletteTray() {
     bubble_->bubble_view()->reset_delegate();
 
   ui::InputDeviceManager::GetInstance()->RemoveObserver(this);
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->RemoveSessionStateObserver(this);
 }