Converted IncognitoForced boolean policy into IncognitoModeAvailability enum policy.

chrome/browser/prefs/incognito_mode_availability_prefs.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/incognito_mode_availability_prefs.h"
+
+#include "base/logging.h"
+
+namespace IncognitoModeAvailabilityPrefs {
+
+bool IntToIngocnitoModeAvailability(int in_value,
+                                    IncognitoModeAvailability* out_value) {
+  DCHECK(out_value);
+  if (in_value < 0 || in_value >= AVAILABILITY_NUM_TYPES) {
+    *out_value = ENABLED;
+    return false;
+  }
+  *out_value = static_cast<IncognitoModeAvailability>(in_value);
+  return true;
+}
+
+}  // namespace IncognitoModeAvailability