Fix the clipboard feature spec.

extensions/common/api/_permission_features.json

 // 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.
 
 // This features file defines permissions for extension APIs implemented
 // under src/extensions.
 
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
@@ skipping 153 matching lines @@
       "FA01E0B81978950F2BC5A50512FD769725F57510",  // Beta
       "B11A93E7E5B541F8010245EBDE2C74647D6C14B9",  // Canary
       "F155646B5D1CA545F7E1E4E20D573DFDD44C2540",  // Google Cast Beta
       "16CA7A47AAE4BE49B1E75A6B960C3875E945B264",  // Google Cast Stable
       "C17CD9E6868D7B9C67926E0EC612EA25C768418F",  // http://crbug.com/457908
       "226CF815E39A363090A1E547D53063472B8279FA"   // http://crbug.com/574889
     ]
   },
   "clipboard": {
     "channel": "dev",
-    "extension_types": ["platform_app"]
+    "extension_types": ["platform_app"],
+    "platforms": ["chromeos"]
   },
   "declarativeWebRequest": {
       "channel": "beta",
       "extension_types": ["extension", "legacy_packaged_app"]
   },
   "diagnostics": [
     {
       "channel": "dev",
       "extension_types": ["platform_app"]
     },
@@ skipping 308 matching lines @@
   }],
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
    },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   }
 }