Move Proxy Settings API 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 4176 matching lines @@
             "properties": {
               "data": { "type": "string", "description": "Additional information." },
               "lastMessage": { "type": "boolean", "description": "True if this was the last message for this test" }
             }
           }
         ]
       }
     ]
   },
   {
-    "namespace": "experimental.proxy",
+    "namespace": "proxy",
     "types": [
       {
         "id": "ProxyServer",
         "type": "object",
         "description": "An object encapsulating a single proxy server's specification.",
         "properties": {
           "scheme": {"type": "string", "optional": true, "enum": ["http", "https", "socks4", "socks5"], "description": "The scheme (protocol) of the proxy server itself. Defaults to 'http'."},
           "host": {"type": "string", "description": "The URI of the proxy server. This must be an ASCII hostname (in Punycode format). IDNA is not supported, yet."},
           "port": {"type": "integer", "optional": true, "description": "The port of the proxy server. Defaults to a port that depends on the scheme."}
         }
@@ skipping 1099 matching lines @@
                 "description": "Passport for passing to proxy."
               }
             ]
           }
         ]
       }
     ],
     "events": []
   },
   {
-    "namespace": "experimental.extension",
+    "namespace": "preferences",
     "types": [
       {
         "id": "Preference",
         "type": "object",
         "customBindings": "Preference",
         "description": "An object which allows access to a preference.",
         "functions": [
           {
             "name": "get",
             "type": "function",
@@ skipping 267 matching lines @@
           {
             "type": "integer",
             "name": "tabId",
             "description": "The id of the tab that was detached."
           }
         ]
       }
     ]
   }
 ]