Move context menu module out of experimental.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 2484 matching lines @@
                 "description": "Details about the tab's process."
               }
             ]
           }
         ]
       }
     ],
     "events": []
   },
   {
-    "namespace": "experimental.contextMenus",
+    "namespace": "contextMenus",
     "types": [],
     "functions": [
       {
         "name": "create",
         "type": "function",
         "description": "Creates a new context menu item. Note that if an error occurs during creation, you may not find out until the creation callback fires (the details will be in chrome.extension.lastError).",
         "returns": {
           "type": "integer",
           "description": "The id of the newly created item."
         },
@@ skipping 659 matching lines @@
       {
         "name": "onInputCancelled",
         "perExtensionEvent": true,
         "type": "function",
         "description": "User has ended the keyword input session without accepting the input.",
         "parameters": []
       }
     ]
   }
 ]