Remove the last usages of PrefObserver outside of Prefs.

chrome/browser/prefs/mock_pref_change_callback.cc

+// Copyright (c) 2011 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.
+
+#include "chrome/browser/prefs/mock_pref_change_callback.h"
+
+#include "base/bind.h"
+#include "chrome/common/chrome_notification_types.h"
+
+MockPrefChangeCallback::MockPrefChangeCallback(PrefServiceBase* prefs)
+    : prefs_(prefs) {
+}
+
+MockPrefChangeCallback::~MockPrefChangeCallback() {}
+
+PrefChangeRegistrar::NamedChangeCallback MockPrefChangeCallback::GetCallback() {
+  return base::Bind(&MockPrefChangeCallback::OnPreferenceChanged,
+                    base::Unretained(this));
+}
+
+void MockPrefChangeCallback::Expect(const std::string& pref_name,
+                                    const Value* value) {
+  EXPECT_CALL(*this, OnPreferenceChanged(pref_name))
+      .With(PrefValueMatches(prefs_, pref_name, value));
+}