Fix classes that have too many virtuals for inline constructors.

chrome/browser/extensions/install_observer.h

 // Copyright 2013 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 CHROME_BROWSER_EXTENSIONS_INSTALL_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_INSTALL_OBSERVER_H_
 
 #include <string>
 
 #include "ui/gfx/image/image_skia.h"
@@ skipping 51 matching lines @@
   // simply forwarded from the chrome::NOTIFICATIONs.
   virtual void OnDisabledExtensionUpdated(const Extension* extension) {}
 
   // Called when the app list is reordered.
   virtual void OnAppsReordered() {}
 
   // Notifies observers that the observed object is going away.
   virtual void OnShutdown() {}
 
  protected:
+  InstallObserver() = default;
   virtual ~InstallObserver() {}
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_INSTALL_OBSERVER_H_