mash: Migrate shelf app list button to wm common types

ash/shell/window_watcher.cc

Index: ash/shell/window_watcher.cc
diff --git a/ash/shell/window_watcher.cc b/ash/shell/window_watcher.cc
index 5254210b7501974dfb480d5eacadc75741cc32e0..64f1bc93bbae7b240d830c71a1e87aab4734e1f2 100644
--- a/ash/shell/window_watcher.cc
+++ b/ash/shell/window_watcher.cc
@@ -9,6 +9,7 @@
 #include "ash/common/shelf/shelf_item_delegate_manager.h"
 #include "ash/common/shelf/shelf_model.h"
 #include "ash/common/shell_window_ids.h"
+#include "ash/common/wm_shell.h"
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shelf/shelf_util.h"
@@ -96,7 +97,7 @@ void WindowWatcher::OnWindowAdded(aura::Window* new_window) {
     return;
 
   static int image_count = 0;
-  ShelfModel* model = Shell::GetInstance()->shelf_model();
+  ShelfModel* model = WmShell::Get()->shelf_model();
   ShelfItem item;
   item.type = new_window->type() == ui::wm::WINDOW_TYPE_PANEL
                   ? ash::TYPE_APP_PANEL
@@ -125,7 +126,7 @@ void WindowWatcher::OnWillRemoveWindow(aura::Window* window) {
   for (IDToWindow::iterator i = id_to_window_.begin(); i != id_to_window_.end();
        ++i) {
     if (i->second == window) {
-      ShelfModel* model = Shell::GetInstance()->shelf_model();
+      ShelfModel* model = WmShell::Get()->shelf_model();
       int index = model->ItemIndexByID(i->first);
       DCHECK_NE(-1, index);
       model->RemoveItemAt(index);