Add stubs for brailleDisplayPrivate extension API.

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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "activeTab": {
     "channel": "stable",
@@ skipping 64 matching lines @@
   },
   "bookmarkManagerPrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"],
     "location": "component"
   },
   "bookmarks": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
+  "brailleDisplayPrivate": {
+    "channel": "dev",
+    "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
+  },

[not at google - send to devlin, 2013/09/03 14:35:35]

you want to whitelist this for chromevox, or at least for component extensions,
right?

[Peter Lundblad, 2013/09/03 23:03:34]

Whitelisted for component apps.

   "browsingData": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "chromePrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"],
     "whitelist": [
       "haiffjcadagjlijoggckpgfnoeiflnem",  // Citrix Receiver
       "gnedhmakppccajfpfiihfcdlnpgomkcf",  // Citrix Receiver Beta
@@ skipping 591 matching lines @@
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "webview": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   }
 }