Revert of Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

chrome/browser/extensions/api/storage/settings_namespace.h

+// Copyright (c) 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.
+
+#ifndef CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_NAMESPACE_H_
+#define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_NAMESPACE_H_
+
+#include <string>
+
+namespace extensions {
+
+namespace settings_namespace {
+
+// The namespaces of the storage areas.
+enum Namespace {
+  LOCAL,    // "local"    i.e. chrome.storage.local
+  SYNC,     // "sync"     i.e. chrome.storage.sync
+  MANAGED,  // "managed"  i.e. chrome.storage.managed
+  INVALID
+};
+
+// Converts a namespace to its string representation.
+// Namespace must not be INVALID.
+std::string ToString(Namespace settings_namespace);
+
+// Converts a string representation of a namespace to its namespace, or INVALID
+// if the string doesn't map to one.
+Namespace FromString(const std::string& ns_string);
+
+}  // namespace settings_namespace
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_NAMESPACE_H_