Remove content::NotificationObserver dependency from most Prefs code.

base/prefs/public/pref_observer.h

Index: base/prefs/public/pref_observer.h
diff --git a/base/prefs/public/pref_observer.h b/base/prefs/public/pref_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..5d9338e1fe088797901c520794e9ae842b7bd239
--- /dev/null
+++ b/base/prefs/public/pref_observer.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_PREFS_PUBLIC_PREF_OBSERVER_H_
+#define BASE_PREFS_PUBLIC_PREF_OBSERVER_H_
+
+#include <string>
+
+class PrefServiceBase;
+
+class PrefObserver {
+ public:

[Mattias Nissler (ping if slow), 2012/10/30 13:37:07]

should have a comment, and you should put a TODO saying that we'd like to
replace that by a base::Callback-style interface.

+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) = 0;

[Mattias Nissler (ping if slow), 2012/10/30 09:09:30]

Any reason to not use base::Callback<void(PrefServiceBase*, const std::string&)
for this purpose? I guess this would also allow for reducing lots of complexity
in the consumers, because they can drop switch(pref_name)-style code and have
dedicated handlers for the different events.

+};
+
+#endif  // BASE_PREFS_PUBLIC_PREF_OBSERVER_H_