Added default implementations of GetAcceleratorForCommandId.

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 ec1be9fbf937b181597d27728ce228ff6b0a3003..3d6e158c95db60b31e462c66653b4fa7fc870811 100644
--- a/ash/shelf/shelf_view_unittest.cc
+++ b/ash/shelf/shelf_view_unittest.cc
@@ -2043,10 +2043,6 @@ class TestShelfMenuModel : public ShelfMenuModel,
   bool IsCommandIdEnabled(int command_id) const override {
     return command_id != 0;
   }
-  bool GetAcceleratorForCommandId(int command_id,
-                                  ui::Accelerator* accelerator) const override {
-    return false;
-  }
   void ExecuteCommand(int command_id, int event_flags) override {}
 
   DISALLOW_COPY_AND_ASSIGN(TestShelfMenuModel);