Handle app custom icon via aura::Window property.

extensions/shell/browser/shell_app_delegate.h

 // Copyright 2014 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 EXTENSIONS_SHELL_BROWSER_SHELL_APP_DELEGATE_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_APP_DELEGATE_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "extensions/browser/app_window/app_delegate.h"
@@ skipping 28 matching lines @@
                       const content::FileChooserParams& params) override;
   void RequestMediaAccessPermission(
       content::WebContents* web_contents,
       const content::MediaStreamRequest& request,
       const content::MediaResponseCallback& callback,
       const Extension* extension) override;
   bool CheckMediaAccessPermission(content::WebContents* web_contents,
                                   const GURL& security_origin,
                                   content::MediaStreamType type,
                                   const Extension* extension) override;
-  int PreferredIconSize() override;
+  int PreferredIconSize() const override;
   void SetWebContentsBlocked(content::WebContents* web_contents,
                              bool blocked) override;
   bool IsWebContentsVisible(content::WebContents* web_contents) override;
   void SetTerminatingCallback(const base::Closure& callback) override;
   void OnHide() override {}
   void OnShow() override {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellAppDelegate);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_APP_DELEGATE_H_