Remove extension process side of chrome.devtools API, it's obsolete.

chrome/test/data/extensions/devtools/timeline_api_two/background_two.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.
-
-var devtoolsTabEvents = undefined;
-
-function pageEventListener() {
-  receivedEvents.push("onPageEvent");
-}
-
-function tabCloseListener() {
-  receivedEvents.push("onTabClose");
-}
-
-function registerListenersForTab(tabId) {
-  devtoolsTabEvents = chrome.devtools.getTabEvents(tabId);
-  devtoolsTabEvents.onPageEvent.addListener(pageEventListener);
-  devtoolsTabEvents.onTabClose.addListener(tabCloseListener);
-  window.domAutomationController.send(true);
-}
-
-function unregisterListeners() {
-  devtoolsTabEvents.onPageEvent.removeListener(pageEventListener);
-  devtoolsTabEvents.onTabClose.removeListener(tabCloseListener);
-  window.domAutomationController.send(true);
-}