[Extensions] Remove the Infobar API

chrome/common/extensions/docs/examples/api/infobars/sandwichbar/background.js

-// Copyright (c) 2013 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.
-
-/**
- * Handles requests sent by the content script.  Shows an infobar.
- */
-function onRequest(request, sender, sendResponse) {
-  // The number of matches is sent in the request - pass it to the
-  // infobar.
-  var url = "infobar.html#" + request.count;
-
-  // Show the infobar on the tab where the request was sent.
-  chrome.infobars.show({
-    tabId: sender.tab.id,
-    path: url
-  });
-
-  // Return nothing to let the connection be cleaned up.
-  sendResponse({});
-};
-
-// Listen for the content script to send a message to the background page.
-chrome.extension.onRequest.addListener(onRequest);