Migrate upgrade notifications to observer

chrome/browser/upgrade_observer.h

Index: chrome/browser/upgrade_observer.h
diff --git a/chrome/browser/upgrade_observer.h b/chrome/browser/upgrade_observer.h
index 51af04f44be214733f080648c818bbe08ae44bef..9cd6e545ed5f5d91330af335d605c3afe22960ed 100644
--- a/chrome/browser/upgrade_observer.h
+++ b/chrome/browser/upgrade_observer.h
@@ -11,7 +11,24 @@ class UpgradeObserver {
  public:
   // Triggered when a software update is available, but downloading requires
   // user's agreement as current connection is cellular.
-  virtual void OnUpdateOverCellularAvailable() = 0;
+  virtual void OnUpdateOverCellularAvailable() {}
+
+  // Triggered when Chrome believes an update has been installed and available
+  // for long enough with the user shutting down to let it take effect. See
+  // upgrade_detector.cc for details on how long it waits. No details are
+  // expected.
+  virtual void OnUpgradeRecommended() {}
+
+  // Triggered when a critical update has been installed. No details are
+  // expected.
+  virtual void OnCriticalUpgradeInstalled() {}
+
+  // Triggered when the current install is outdated. No details are expected.
+  virtual void OnOutdatedInstall() {}
+
+  // Triggered when the current install is outdated and auto-update (AU) is
+  // disabled. No details are expected.
+  virtual void OnOutdatedInstallNoAU() {}
 
  protected:
   virtual ~UpgradeObserver() {}