mash: Refactor ChromeLauncherController's ShelfDelegate code.

ash/shelf/shelf_view_unittest.cc

Index: ash/shelf/shelf_view_unittest.cc
diff --git a/ash/shelf/shelf_view_unittest.cc b/ash/shelf/shelf_view_unittest.cc
index 5b374ef2105805552390c501a22cd8cfc8559a0e..d077d3eb029fb23c905411c69c529c5fafb5cd29 100644
--- a/ash/shelf/shelf_view_unittest.cc
+++ b/ash/shelf/shelf_view_unittest.cc
@@ -263,8 +263,6 @@ class TestShelfDelegateForShelfView : public TestShelfDelegate {
     return base::checked_cast<ShelfID>(id);
   }
 
-  bool HasShelfIDToAppIDMapping(ShelfID id) const override { return true; }
-
   const std::string& GetAppIDForShelfID(ShelfID id) override {
     // Use |app_id_| member variable because returning a reference to local
     // variable is not allowed.