Remove windows.onCreated hack from Keep Awake extension.

The example extension for the chrome.power API registered a
listener for windows.onCreated to work around an issue where
runtime.onStartup didn't fire on Chrome OS. The underlying
Chrome bug has been fixed now, so the windows.onCreated
workaround is no longer needed.

BUG=222473
TEST=install the extension on Chrome OS and check that
     /var/log/power_manager/powerd.LATEST reports an
     extension-driven policy change when logging in

Review URL: https://codereview.chromium.org/531953002

Cr-Commit-Position: refs/heads/master@{#293043}

chrome/common/extensions/docs/examples/api/power/background.js

@@ -95,8 +95,3 @@ chrome.browserAction.onClicked.addListener(function() {
 chrome.runtime.onStartup.addListener(function() {
   loadSavedState(function(state) { setState(state); });
 });
-
-// TODO(derat): Remove this once http://crbug.com/222473 is fixed.
-chrome.windows.onCreated.addListener(function() {
-  loadSavedState(function(state) { setState(state); });
-});

chrome/common/extensions/docs/examples/api/power/manifest.json

@@ -3,7 +3,7 @@
 
   "name": "__MSG_extensionName__",
   "description": "__MSG_extensionDescription__",
-  "version": "1.7",
+  "version": "1.8",
   "icons": {
     "16": "images/icon-16.png",
     "48": "images/icon-48.png",