Move Proxy Settings API out of experimental

chrome/test/data/extensions/api_test/proxy/system/test.js

 // Copyright (c) 2011 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.
 
 // proxy api test
 // browser_tests.exe --gtest_filter=ProxySettingsApiTest.ProxySystem
 
 chrome.test.runTests([
   // Verify that execution has started to make sure flaky timeouts are not
   // caused by us.
   function verifyTestsHaveStarted() {
     chrome.test.succeed();
   },
   function setSystemProxy() {
     var config = { mode: "system" };
-    chrome.experimental.proxy.settings.set(
+    chrome.proxy.settings.set(
         {'value': config},
         chrome.test.callbackPass());
   }
 ]);