Restrict the File System Provier API permission to Chrome OS only.

chrome/common/extensions/api/_permission_features.json

 // 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.
 
 // This features file defines permissions for extension APIs implemented
 // under src/chrome.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
@@ skipping 451 matching lines @@
       "2FC374607C2DF285634B67C64A2E356C607091C3",  // Quickoffice
       "3727DD3E564B6055387425027AD74C58784ACC15",  // Quickoffice internal
       "12E618C3C6E97495AAECF2AC12DEB082353241C6",  // QO component extension
       "D5736E4B5CF695CB93A2FB57E4FDC6E5AFAB6FE2",  // http://crbug.com/312900
       "D57DE394F36DC1C3220E7604C575D29C51A6C495",  // http://crbug.com/319444
       "3F65507A3B39259B38C8173C6FFA3D12DF64CCE9"   // http://crbug.com/371562
     ]
   }],
   "fileSystemProvider": {
     "channel": "dev",
-    "extension_types": ["extension", "platform_app"]
+    "extension_types": ["extension", "platform_app"],
+    "platforms": ["chromeos"]
   },
   "firstRunPrivate": {
     "channel": "stable",
     "extension_types": ["platform_app"],
     "location": "component",
     "platforms": ["chromeos"]
   },
   "fontSettings": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
@@ skipping 576 matching lines @@
   },
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   }
 }