Replace chrome::NOTIFICATION_EXTENSION_WARNING_CHANGED message with observer pattern

chrome/browser/extensions/extension_warning_set.h

Index: chrome/browser/extensions/extension_warning_set.h
diff --git a/chrome/browser/extensions/extension_warning_set.h b/chrome/browser/extensions/extension_warning_set.h
index d2032117bcb920f57114c9beb917daafd7124669..96d02b39bb9899e2c1c15225802c15b6e0212a04 100644
--- a/chrome/browser/extensions/extension_warning_set.h
+++ b/chrome/browser/extensions/extension_warning_set.h
@@ -11,6 +11,7 @@
 
 #include "base/memory/linked_ptr.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/observer_list.h"
 #include "base/string16.h"
 #include "base/threading/non_thread_safe.h"
 #include "googleurl/src/gurl.h"
@@ -135,6 +136,11 @@ class ExtensionWarningSet {
 // them. This class must be used on the UI thread only.
 class ExtensionWarningService : public base::NonThreadSafe {
  public:
+  class Observer {
+   public:
+    virtual void ExtensionWarningsChanged() = 0;
+  };
+
   // |profile| may be NULL for testing. In this case, be sure to not insert
   // any warnings.
   explicit ExtensionWarningService(Profile* profile);
@@ -174,6 +180,9 @@ class ExtensionWarningService : public base::NonThreadSafe {
       void* profile_id,
       scoped_ptr<ExtensionWarningSet> warnings);
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
  protected:
   // Virtual for testing.
   virtual void NotifyWarningsChanged();
@@ -194,6 +203,8 @@ class ExtensionWarningService : public base::NonThreadSafe {
   std::set<linked_ptr<ExtensionWarning> > badge_suppressions_;
 
   Profile* profile_;
+
+  ObserverList<Observer> observer_list_;
 };
 
 }  // namespace extensions