mash: Migrate shelf app list button to wm common types

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 781f8b465f687b492b1e681039cdb8d494076353..8577b9992b07ac03017d380d803ae6717bc47d6b 100644
--- a/ash/metrics/user_metrics_recorder.cc
+++ b/ash/metrics/user_metrics_recorder.cc
@@ -161,8 +161,7 @@ void RecordShelfItemCounts() {
   int pinned_item_count = 0;
   int unpinned_item_count = 0;
 
-  for (const ShelfItem& shelf_item :
-       Shell::GetInstance()->shelf_model()->items()) {
+  for (const ShelfItem& shelf_item : WmShell::Get()->shelf_model()->items()) {
     if (shelf_item.type != TYPE_APP_LIST) {
       // Internal ash apps do not have an app id and thus will always be counted
       // as unpinned.