Add documentation for the chrome.sockets API and manifest key.

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.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
 //
 // $ echo -n "aaaabbbbccccddddeeeeffffgggghhhh" | \
@@ skipping 743 matching lines @@
   }, {
     "channel": "stable",
     "extension_types": ["extension"],
     "whitelist": [
       // The connectivity diagnostic utility is a component extension that is
       // used to try to provide suggestions on how to fix connection issues.  It
       // should be the only non-app allowed to use the socket API.
       "32A1BA997F8AB8DE29ED1BA94AAF00CF2A3FEFA7"
     ]
   }],
-  "sockets.udp": {

[not at google - send to devlin, 2014/01/03 00:24:41]

Could you submit these non-documentation changes separately? It's easier for
patch history, dcommitting, sherrifs, figuring out breakages, etc.

[rpaquay, 2014/01/06 22:28:29]

Done.

-    "channel": "dev",
-    "extension_types": ["platform_app"]
-  },
   "syncFileSystem": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
   "systemIndicator": {
     "channel": "dev",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
   },
   "storage": {
     "channel": "stable",
@@ skipping 159 matching lines @@
     // Only allowed for whitelisted extensions until all the caveats are
     // addressed. Tracked in crbug/285151.
     "channel": "stable",
     "extension_types": ["extension"],
     "location": "component",
     "whitelist": [
       "D519188F86D9ACCEE0412007B227D9936EB9676B"  // GAIA Component Extension
     ]
   }]
 }