Add 'ready-for-update-on-quit' event for auto-updater.

browser/auto_updater_delegate.h

@@ -13,9 +13,14 @@ namespace auto_updater {
 
 class AutoUpdaterDelegate {
  public:
+  // The application is going to relaunch to install update.
   virtual void WillInstallUpdate(const std::string& version,
                                  const base::Closure& install);
 
+  // User has chosen to update on quit.
+  virtual void ReadyForUpdateOnQuit(const std::string& version,
+                                    const base::Closure& quit_and_install);
+
  protected:
   virtual ~AutoUpdaterDelegate() {}
 };