Moves maintaining root_window_for_new_windows_ to Shell

ash/common/scoped_root_window_for_new_windows.cc

Index: ash/common/scoped_root_window_for_new_windows.cc
diff --git a/ash/common/scoped_root_window_for_new_windows.cc b/ash/common/scoped_root_window_for_new_windows.cc
index 28e24f00f6a7c0b9efe26e2b924d2e1278a5802e..55c59d20328a95458918d45ace02ac7c70255ef2 100644
--- a/ash/common/scoped_root_window_for_new_windows.cc
+++ b/ash/common/scoped_root_window_for_new_windows.cc
@@ -4,7 +4,7 @@
 
 #include "ash/common/scoped_root_window_for_new_windows.h"
 
-#include "ash/common/wm_shell.h"
+#include "ash/shell.h"
 #include "base/logging.h"
 
 namespace ash {
@@ -12,11 +12,11 @@ namespace ash {
 ScopedRootWindowForNewWindows::ScopedRootWindowForNewWindows(
     WmWindow* new_root) {
   DCHECK(new_root);
-  WmShell::Get()->scoped_root_window_for_new_windows_ = new_root;
+  Shell::GetInstance()->scoped_root_window_for_new_windows_ = new_root;
 }
 
 ScopedRootWindowForNewWindows::~ScopedRootWindowForNewWindows() {
-  WmShell::Get()->scoped_root_window_for_new_windows_ = nullptr;
+  Shell::GetInstance()->scoped_root_window_for_new_windows_ = nullptr;
 }
 
 }  // namespace ash