[fsp] Enable the File System Provider API for extensions.

chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_apitest.cc

 // Copyright 2013 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/extensions/extension_apitest.h"
 
 namespace extensions {
 
 class FileSystemProviderApiTest : public ExtensionApiTest {
  public:
@@ skipping 102 matching lines @@
                                           kFlagLoadAsComponent))
       << message_;
 }
 
 IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, WriteFile) {
   ASSERT_TRUE(RunPlatformAppTestWithFlags("file_system_provider/write_file",
                                           kFlagLoadAsComponent))
       << message_;
 }
 
+IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, Extension) {
+  ASSERT_TRUE(RunPlatformAppTestWithFlags("file_system_provider/extension",
+                                          kFlagLoadAsComponent))
+      << message_;
+}
+
 }  // namespace extensions