Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

extensions/browser/api/extensions_api_client.h

Index: extensions/browser/api/extensions_api_client.h
diff --git a/extensions/browser/api/extensions_api_client.h b/extensions/browser/api/extensions_api_client.h
new file mode 100644
index 0000000000000000000000000000000000000000..ead48259171bdd2c2bcdd5df56870f11b8934b9e
--- /dev/null
+++ b/extensions/browser/api/extensions_api_client.h
@@ -0,0 +1,52 @@
+// Copyright 2014 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 EXTENSIONS_BROWSER_API_EXTENSIONS_API_CLIENT_H_
+#define EXTENSIONS_BROWSER_API_EXTENSIONS_API_CLIENT_H_
+
+#include <map>
+
+#include "base/memory/ref_counted.h"
+#include "extensions/browser/api/storage/settings_namespace.h"
+
+template <class T>
+class ObserverListThreadSafe;
+
+namespace content {
+class BrowserContext;
+}
+
+namespace extensions {
+
+class SettingsObserver;
+class SettingsStorageFactory;
+class ValueStoreCache;
+
+// Allows embedders of the extensions module to customize their support for
+// API features.
+class ExtensionsApiClient {
+ public:
+  ExtensionsApiClient();
+  virtual ~ExtensionsApiClient();
+
+  // Storage API support.
+
+  // Add any additional value store caches (e.g. for chrome.storage.managed)
+  // to |caches|. By default adds nothing.
+  virtual void AddAdditionalValueStoreCaches(
+      content::BrowserContext* context,
+      scoped_refptr<SettingsStorageFactory> factory,
+      scoped_refptr<ObserverListThreadSafe<SettingsObserver> > observers,
+      std::map<settings_namespace::Namespace, ValueStoreCache*>* caches);
+
+  // Returns the single instance of |this|.
+  static ExtensionsApiClient* Get();
+
+  // Initializes the single instance. Does not take ownership.
+  static void Set(ExtensionsApiClient* client);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_API_EXTENSIONS_API_CLIENT_H_