Add tabs.onReplaced event to notify listeners of tabs being swapped due to prerendering or instant.

chrome/test/data/extensions/api_test/tabs/on_replaced/test_onreplaced.js

+// Copyright (c) 2012 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.
+
+onload = function() {
+  chrome.test.getConfig(function(config) {
+    chrome.tabs.create({"url": "about:blank"}, function(tab) {
+      chrome.test.runTests([
+          function onReplacedEvent() {
+            var tabId = tab.id;
+
+            var onReplaceListener = function(new_tab_id, old_tab_id) {
+              chrome.test.assertTrue(tabId != new_tab_id);
+              chrome.test.assertEq(tabId, old_tab_id);
+              chrome.tabs.onReplaced.removeListener(onReplaceListener);
+              chrome.test.succeed();
+            };
+            chrome.tabs.onReplaced.addListener(onReplaceListener);
+
+            var URL_TARGET =
+                "http://127.0.0.1:PORT/files/prerender/prerender_page.html"
+                    .replace(/PORT/g, config.testServer.port);
+            chrome.tabs.update({
+              url: URL_TARGET
+            });
+
+            chrome.test.notifyPass();
+          }
+      ]);
+    });
+  });
+};