Promotes more accessors from WmShell to Shell

ash/common/system/overview/overview_button_tray.cc

Index: ash/common/system/overview/overview_button_tray.cc
diff --git a/ash/common/system/overview/overview_button_tray.cc b/ash/common/system/overview/overview_button_tray.cc
index d642efe8a971141022091874d4c611162cc98eb6..8eaeaf8a7513afefed9d4d41d6d5771b3c0bbfe9 100644
--- a/ash/common/system/overview/overview_button_tray.cc
+++ b/ash/common/system/overview/overview_button_tray.cc
@@ -48,7 +48,7 @@ void OverviewButtonTray::UpdateAfterLoginStatusChange(LoginStatus status) {
 
 bool OverviewButtonTray::PerformAction(const ui::Event& event) {
   WindowSelectorController* controller =
-      WmShell::Get()->window_selector_controller();
+      Shell::Get()->window_selector_controller();
   // Toggling overview mode will fail if there is no window to show.
   bool performed = controller->ToggleOverview();
   WmShell::Get()->RecordUserMetricsAction(UMA_TRAY_OVERVIEW);