Exclude experimental.socket from documentation.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
           "tab": {"$ref": "Tab", "optional": true, "description":"This property will <b>only</b> be present when the connection was opened from a tab or content script."},
@@ skipping 9155 matching lines @@
                 }
               }
             ]
           }
         ]
       }
     ]
   },
   {
     "namespace": "experimental.socket",
+    "nodoc": true,
     "types": [
       {
         "id": "SocketEvent",
         "type": "object",
         "description": "A socket event.",
         "properties": {
           "type": {
             "type": "string",
             "enum": ["data", "error"],
             "description": "A 'data' event represents data received on the socket. An 'error' event represents an error."
@@ skipping 195 matching lines @@
                 "enum": ["enabled", "disabled", "forced"],
                 "description": "Exposes whether the incognito mode is available to windows. One of 'enabled', 'disabled' (user cannot browse pages in Incognito mode), 'forced' (all pages/sessions are forced into Incognito mode)."
               }
             ]
           }
         ]
       }
     ]
   }
 ]