reland: mash: Remove ChromeLauncherController's |id_to_item_controller_map_|.

chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc

Index: chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc
diff --git a/chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc b/chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc
index e7594c473523b21a90da87c02902b3009e047d63..2f452268a2c63f9db7d2b05567f612742efc1ed5 100644
--- a/chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc
+++ b/chrome/browser/ui/ash/launcher/arc_app_launcher_browsertest.cc
@@ -4,6 +4,7 @@
 
 #include "ash/public/cpp/shelf_item_delegate.h"
 #include "ash/shelf/shelf_delegate.h"
+#include "ash/shelf/shelf_model.h"
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
 #include "base/macros.h"
@@ -259,9 +260,7 @@ class ArcAppLauncherBrowserTest : public ExtensionBrowserTest {
 
   ash::ShelfItemDelegate* GetAppItemController(const std::string& id) {
     const ash::ShelfID shelf_id = shelf_delegate()->GetShelfIDForAppID(id);
-    if (!shelf_id)
-      return nullptr;
-    return chrome_controller()->GetShelfItemDelegate(shelf_id);
+    return ash::Shell::Get()->shelf_model()->GetShelfItemDelegate(shelf_id);
   }
 
   ArcAppListPrefs* app_prefs() { return ArcAppListPrefs::Get(profile()); }