Fix classes that have too many virtuals for inline constructors.

ash/shell_observer.h

 // Copyright (c) 2012 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.
 
 #ifndef ASH_SHELL_OBSERVER_H_
 #define ASH_SHELL_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/system/user/login_status.h"
 
@@ skipping 49 matching lines @@
   virtual void OnMaximizeModeStarted() {}
 
   // Called when the always maximize mode has ended. Windows may still be
   // animating but have been restored.
   virtual void OnMaximizeModeEnded() {}
 
   // Called at the end of Shell::Init.
   virtual void OnShellInitialized() {}
 
  protected:
+  ShellObserver() = default;
   virtual ~ShellObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_OBSERVER_H_