Settings Overides -- warn user when extensions override their NTP.

extensions/browser/extension_prefs.h

Index: extensions/browser/extension_prefs.h
diff --git a/extensions/browser/extension_prefs.h b/extensions/browser/extension_prefs.h
index 90a9b835d5d3fda032741b75b2df1d4290a2badd..d2cc9ebc4277849faf60e50a7cc38c3cd22e2e91 100644
--- a/extensions/browser/extension_prefs.h
+++ b/extensions/browser/extension_prefs.h
@@ -323,6 +323,12 @@ class ExtensionPrefs : public ExtensionScopedPrefs, public KeyedService {
   void SetSettingsApiBubbleBeenAcknowledged(const std::string& extension_id,
                                             bool value);
 
+  // Whether the user has been notified about extension with |extension_id|
+  // overriding the new tab page.
+  bool HasNtpOverriddenBubbleBeenAcknowledged(const std::string& extension_id);
+  void SetNtpOverriddenBubbleBeenAcknowledged(const std::string& extension_id,
+                                              bool value);
+
   // Returns true if the extension notification code has already run for the
   // first time for this profile. Currently we use this flag to mean that any
   // extensions that would trigger notifications should get silently