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

Previously, only apps were allowed to use this api, however most clients will
be actually written as extensions.

TEST=browser_tests: *FileSystemProvider*Extension*
BUG=409487

Review URL: https://codereview.chromium.org/527663002

Cr-Commit-Position: refs/heads/master@{#293100}

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

@@ -120,4 +120,10 @@ IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, WriteFile) {
       << message_;
 }
 
+IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, Extension) {
+  ASSERT_TRUE(RunPlatformAppTestWithFlags("file_system_provider/extension",
+                                          kFlagLoadAsComponent))
+      << message_;
+}
+
 }  // namespace extensions

chrome/common/extensions/api/_permission_features.json

@@ -559,7 +559,7 @@
   }],
   "fileSystemProvider": {
     "channel": "dev",
-    "extension_types": ["platform_app"]
+    "extension_types": ["extension", "platform_app"]
   },
   "firstRunPrivate": {
     "channel": "stable",

chrome/common/extensions/docs/templates/public/extensions/fileSystemProvider.html

+{{+partials.standard_extensions_api api:apis.extensions.fileSystemProvider intro:intros.fileSystemProvider/}}

chrome/test/data/extensions/api_test/file_system_provider/extension/manifest.json

+{
+  "key": "MIGdMA0GCSqGSIb3DQEBAQUAA4GLADCBhwKBgQDOuXEIuoK1kAkBe0SKiJn/N9oNn3oUxGa4dwj40MnJqPn+w0aR2vuyocm0R4Drp67aYwtLjOVPF4CICRq6ICP6eU07gGwQxGdZ7HJASXV8hm0tab5I70oJmRLfFJyVAMCeWlFaOGq05v2i6EbifZM0qO5xALKNGQt+yjXi5INM5wIBIw==",
+  "name": "chrome.fileSystemProvider.mount in extensions",
+  "version": "0.1",
+  "manifest_version": 2,
+  "description": "Test for chrome.fileSystemProvider.mount() in an extension.",
+  "permissions": ["fileSystemProvider", "fileBrowserPrivate"],
+  "background": {
+    "persistent": false,
+    "scripts": [
+      "chrome-extension://gfnblenhaahcnmfdbebgincjohfkbnch/test_util.js",
+      "test.js"
+    ]
+  }
+}

chrome/test/data/extensions/api_test/file_system_provider/extension/test.js

+// 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.
+
+'use strict';
+
+chrome.test.runTests([
+  // Tests if mounting succeeds when invoked from an extension. Note that all
+  // other tests are implemented as apps.
+  function mount() {
+    var onTestSuccess = chrome.test.callbackPass();
+    chrome.fileSystemProvider.mount(
+        {fileSystemId: 'file-system-id', displayName: 'file-system-name'},
+        function() {
+          onTestSuccess();
+        },
+        function(error) {
+          chrome.test.fail();
+        });
+  },
+]);