ash: Remove ash::Shelf in favor of ash::WmShelf

ash/metrics/user_metrics_recorder.cc

Index: ash/metrics/user_metrics_recorder.cc
diff --git a/ash/metrics/user_metrics_recorder.cc b/ash/metrics/user_metrics_recorder.cc
index 2b22a56a70f854bf5579ae8ad5fc40ee5cc7520c..54290d68167ef5d543d80e712ce342b76e1c73e4 100644
--- a/ash/metrics/user_metrics_recorder.cc
+++ b/ash/metrics/user_metrics_recorder.cc
@@ -13,7 +13,6 @@
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/wm/window_state.h"
-#include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/metrics/desktop_task_switch_metric_recorder.h"
@@ -596,10 +595,7 @@ void UserMetricsRecorder::OnShellShuttingDown() {
 }
 
 void UserMetricsRecorder::RecordPeriodicMetrics() {
-  WmShelf* shelf = WmShell::Get()
-                       ->GetPrimaryRootWindow()
-                       ->GetRootWindowController()
-                       ->GetShelf();
+  WmShelf* shelf = WmShelf::ForWindow(WmShell::Get()->GetPrimaryRootWindow());
   // TODO(bruthig): Investigating whether the check for |manager| is necessary
   // and add tests if it is.
   if (shelf) {