mash: Remove StatusAreaWidget references from system tray classes

ash/system/overview/overview_button_tray.cc

Index: ash/system/overview/overview_button_tray.cc
diff --git a/ash/system/overview/overview_button_tray.cc b/ash/system/overview/overview_button_tray.cc
index 106632d35c47e45cfbdae19b9f9ed6c085b0c912..f7cb2e120d3b601fb0149612e9d79818371d2e12 100644
--- a/ash/system/overview/overview_button_tray.cc
+++ b/ash/system/overview/overview_button_tray.cc
@@ -14,7 +14,6 @@
 #include "ash/common/wm/overview/window_selector_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/shell.h"
-#include "ash/system/status_area_widget.h"
 #include "ash/wm/maximize_mode/maximize_mode_controller.h"
 #include "grit/ash_resources.h"
 #include "grit/ash_strings.h"
@@ -38,8 +37,8 @@ const int kVerticalShelfVerticalPadding = 5;
 
 namespace ash {
 
-OverviewButtonTray::OverviewButtonTray(StatusAreaWidget* status_area_widget)
-    : TrayBackgroundView(status_area_widget->wm_shelf()), icon_(nullptr) {
+OverviewButtonTray::OverviewButtonTray(WmShelf* wm_shelf)
+    : TrayBackgroundView(wm_shelf), icon_(nullptr) {
   SetContentsBackground();
 
   icon_ = new views::ImageView();