[Extensions Mac] Implement developer mode warning on mac

chrome/browser/extensions/extension_message_bubble.h

Index: chrome/browser/extensions/extension_message_bubble.h
diff --git a/chrome/browser/extensions/extension_message_bubble.h b/chrome/browser/extensions/extension_message_bubble.h
index 3819a82f8c169280f2c8b17d711a9fa7bf517500..76986f7a02a8301e9c6e3b5a91c30b097aba0757 100644
--- a/chrome/browser/extensions/extension_message_bubble.h
+++ b/chrome/browser/extensions/extension_message_bubble.h
@@ -11,12 +11,15 @@ class Browser;
 
 namespace extensions {
 
-// The interface between the SuspiciousExtensionBubble bubble and its
-// controller.
+// The interface between an extension message bubble's view and its
+// corresponding ExtensionMessageBubbleController.
 class ExtensionMessageBubble {
  public:
   // Instruct the bubble to appear.
   virtual void Show() = 0;
+
+ protected:
+  virtual ~ExtensionMessageBubble() {}
 };
 
 }  // namespace extensions