Draft change to use base::Closure instead of PrefObserver in PrefChangeRegistrar.

base/prefs/public/pref_change_registrar.cc

Index: base/prefs/public/pref_change_registrar.cc
diff --git a/base/prefs/public/pref_change_registrar.cc b/base/prefs/public/pref_change_registrar.cc
index 3f94b044d8633e0a007bfe196287b9eb3b0b1a1f..1bd3d1aa2f17fc5ff9ffe705fc527751dbb79071 100644
--- a/base/prefs/public/pref_change_registrar.cc
+++ b/base/prefs/public/pref_change_registrar.cc
@@ -4,7 +4,9 @@
 
 #include "base/prefs/public/pref_change_registrar.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/prefs/public/pref_service_base.h"
 
 PrefChangeRegistrar::PrefChangeRegistrar() : service_(NULL) {}
@@ -23,6 +25,11 @@ void PrefChangeRegistrar::Init(PrefServiceBase* service) {
 }
 
 void PrefChangeRegistrar::Add(const char* path, PrefObserver* obs) {
+  return Add(path, base::Bind(&PrefObserver::OnPreferenceChanged,
+                              base::Unretained(obs), service_, path));
+}
+
+void PrefChangeRegistrar::Add(const char* path, const base::Closure& obs) {
   if (!service_) {
     NOTREACHED();
     return;
@@ -37,6 +44,14 @@ void PrefChangeRegistrar::Add(const char* path, PrefObserver* obs) {
 }
 
 void PrefChangeRegistrar::Remove(const char* path, PrefObserver* obs) {
+  // Need to bind the callback the exact same way, although it will
+  // never be called, so that it matches the callback bound via
+  // AddPrefObserver.
+  return Remove(path, base::Bind(&PrefObserver::OnPreferenceChanged,
+                                 base::Unretained(obs), service_, path));

[Mattias Nissler (ping if slow), 2012/11/06 13:26:48]

Hm, comparing callbacks... not sure whether that's a good idea.

In the discussion with battre@ last week, we figured we'd probably change the
interface here to allow only a single callback per pref (we thought that's a
reasonable restriction, haven't checked all consumers though). Also we'd change
the model to not forward the callback registration with PrefService, but store a
std::map<std::string, base::Closure> in PrefChangeRegistrar. We would then have
PrefService keep a list of PrefChangeRegistrars, which it forwards pref change
events to, and PrefChangeRegistrar would figure out the callback to invoke using
its map. Remove would not take a closure as a parameter. WDYT? Makes sense?

+}
+
+void PrefChangeRegistrar::Remove(const char* path, const base::Closure& obs) {
   if (!service_) {
     NOTREACHED();
     return;