Make the hcsm and its providers communicate via an observer interface.

chrome/browser/content_settings/host_content_settings_map.h

Index: chrome/browser/content_settings/host_content_settings_map.h
diff --git a/chrome/browser/content_settings/host_content_settings_map.h b/chrome/browser/content_settings/host_content_settings_map.h
index 10fda1015b573594448d6eae47d11e1b4ac4d62e..e7ec1ca3f91c0c3c4cffaeef9606b2122ea655df 100644
--- a/chrome/browser/content_settings/host_content_settings_map.h
+++ b/chrome/browser/content_settings/host_content_settings_map.h
@@ -19,6 +19,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "chrome/browser/content_settings/content_settings_pattern.h"
+#include "chrome/browser/content_settings/content_settings_observer.h"
 #include "chrome/browser/prefs/pref_change_registrar.h"
 #include "chrome/common/content_settings.h"
 #include "content/browser/browser_thread.h"
@@ -38,7 +39,8 @@ class PrefService;
 class Profile;
 
 class HostContentSettingsMap
-    : public NotificationObserver,
+    : public content_settings::Observer,
+      public NotificationObserver,
       public base::RefCountedThreadSafe<HostContentSettingsMap> {
  public:
   typedef Tuple3<ContentSettingsPattern, ContentSetting, std::string>
@@ -190,6 +192,13 @@ class HostContentSettingsMap
   // thread should be called anymore.
   void ShutdownOnUIThread();
 
+  // content_settings::Observer implementation.
+  virtual void OnContentSettingChanged(
+      ContentSettingsPattern primary_pattern,
+      ContentSettingsPattern secondary_pattern,
+      ContentSettingsType content_type,
+      std::string resource_identifier);
+
   // NotificationObserver implementation.
   virtual void Observe(int type,
                        const NotificationSource& source,