Remove the last usages of PrefObserver outside of Prefs.

chrome/browser/api/prefs/pref_member.h

Index: chrome/browser/api/prefs/pref_member.h
diff --git a/chrome/browser/api/prefs/pref_member.h b/chrome/browser/api/prefs/pref_member.h
index 1441320893210e203966032657a96ca01be1b49a..4b5a63b9d2322e36bb5d77a8ef0ffe4eee013d96 100644
--- a/chrome/browser/api/prefs/pref_member.h
+++ b/chrome/browser/api/prefs/pref_member.h
@@ -103,6 +103,7 @@ class PrefMemberBase : public PrefObserver {
   // See PrefMember<> for description.
   void Init(const char* pref_name, PrefServiceBase* prefs,
             const NamedChangeCallback& observer);
+  void Init(const char* pref_name, PrefServiceBase* prefs);

[Mattias Nissler (ping if slow), 2012/12/04 10:10:34]

So this wasn't used previously? ;)

Any reason to expose this? Can't we just have the consumer below pass a
NamedChangeCallback() as before?

[Jói, 2012/12/04 10:55:57]

It's a performance optimization; we already create a do-nothing
NamedChangeCallback in the constructor of PrefMemberBase, no need to do it
again.

[Mattias Nissler (ping if slow), 2012/12/04 11:18:33]

Is the difference measurable? I usually prefer less/simpler code over premature
optimizations :)

[Jói, 2012/12/04 11:42:26]

The performance difference is probably not measurable except by a targeted
microbenchmark.  OTOH, I don't really feel this version of the code is more
complex, and it avoids some unnecessary work.  Up to you, let me know if you
prefer I get rid of the two-parameter PrefMemberBase::Init.

[Mattias Nissler (ping if slow), 2012/12/04 15:24:37]

I don't feel too strong, feel free to keep as is.

 
   virtual void CreateInternal() const = 0;
 
@@ -178,17 +179,6 @@ class PrefMember : public subtle::PrefMemberBase {
     subtle::PrefMemberBase::Init(pref_name, prefs);
   }
 
-  // Deprecated version of Init.
-  void Init(const char* pref_name, PrefServiceBase* prefs,
-            PrefObserver* observer) {
-    if (observer) {
-      Init(pref_name, prefs, base::Bind(&PrefObserver::OnPreferenceChanged,
-                                        base::Unretained(observer), prefs));
-    } else {
-      Init(pref_name, prefs, NamedChangeCallback());
-    }
-  }
-
   // Unsubscribes the PrefMember from the PrefService. After calling this
   // function, the PrefMember may not be used any more on the UI thread.
   // Assuming |MoveToThread| was previously called, |GetValue|, |IsManaged|,