app_shell: Remove some NOTIMPLEMENTED from ShellNativeAppWindow

extensions/browser/app_window/app_delegate.h

Index: extensions/browser/app_window/app_delegate.h
diff --git a/extensions/browser/app_window/app_delegate.h b/extensions/browser/app_window/app_delegate.h
index 2d5fa1deb33dfdfea9324fd5e0dcba0842d25a22..7961f2afa4d0700b43e4c56809c049b129fa3372 100644
--- a/extensions/browser/app_window/app_delegate.h
+++ b/extensions/browser/app_window/app_delegate.h
@@ -68,6 +68,9 @@ class AppDelegate {
                                           content::MediaStreamType type,
                                           const Extension* extension) = 0;
   virtual int PreferredIconSize() = 0;
+
+  // TODO(jamescook): Eliminate this method. All implementations load the same
+  // icon, and the icon is available in the extensions module resources.
   virtual gfx::ImageSkia GetAppDefaultIcon() = 0;
 
   // Web contents modal dialog support.