[iOS] Upstream observer bridges

ios/chrome/browser/prefs/pref_observer_bridge.mm

Index: ios/chrome/browser/prefs/pref_observer_bridge.mm
diff --git a/ios/chrome/browser/prefs/pref_observer_bridge.mm b/ios/chrome/browser/prefs/pref_observer_bridge.mm
new file mode 100644
index 0000000000000000000000000000000000000000..ebd82f78e7d39b692b4bf86ec25c7157724c7028
--- /dev/null
+++ b/ios/chrome/browser/prefs/pref_observer_bridge.mm
@@ -0,0 +1,27 @@
+// Copyright 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.
+
+#import "ios/chrome/browser/prefs/pref_observer_bridge.h"
+
+#include "base/bind.h"
+#include "base/prefs/pref_change_registrar.h"
+
+PrefObserverBridge::PrefObserverBridge(id<PrefObserverDelegate> delegate)
+    : delegate_(delegate) {
+}
+
+PrefObserverBridge::~PrefObserverBridge() {
+}
+
+void PrefObserverBridge::ObserveChangesForPreference(
+    const std::string& pref_name,
+    PrefChangeRegistrar* registrar) {
+  PrefChangeRegistrar::NamedChangeCallback callback = base::Bind(
+      &PrefObserverBridge::OnPreferenceChanged, base::Unretained(this));
+  registrar->Add(pref_name.c_str(), callback);
+}
+
+void PrefObserverBridge::OnPreferenceChanged(const std::string& pref_name) {
+  [delegate_ onPreferenceChanged:pref_name];
+}