Drop unnecessary override of OnWindowBoundsChanged in NativeWidgetMus::MusWindowObserver

ui/platform_window/stub/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 component("stub") {
   output_name = "stub_window"
 
   deps = [
+    "//base",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/platform_window",
   ]
 
   defines = [ "STUB_WINDOW_IMPLEMENTATION" ]
 
   sources = [
     "stub_window.cc",
     "stub_window.h",
     "stub_window_export.h",
   ]
 }