Make chrome.power sample extension work across updates.

Make the "Keep Awake" extension load its saved state in
response to chrome.runtime.onInstalled in addition to
onStartup. Otherwise, it releases its wake locks after being
upgraded and fails to reacquire them until the next time
Chrome is restarted.

BUG=none
TBR=miket@chromium.org

Review URL: https://codereview.chromium.org/584033003

Cr-Commit-Position: refs/heads/master@{#295805}

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

@@ -95,3 +95,7 @@ chrome.browserAction.onClicked.addListener(function() {
 chrome.runtime.onStartup.addListener(function() {
   loadSavedState(function(state) { setState(state); });
 });
+
+chrome.runtime.onInstalled.addListener(function(details) {
+  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": "1.8",
+  "version": "1.9",
   "icons": {
     "16": "images/icon-16.png",
     "48": "images/icon-48.png",