Use mojo volume interfaces for mash and classic ash.

chrome/browser/chromeos/chrome_browser_main_chromeos.h

Index: chrome/browser/chromeos/chrome_browser_main_chromeos.h
diff --git a/chrome/browser/chromeos/chrome_browser_main_chromeos.h b/chrome/browser/chromeos/chrome_browser_main_chromeos.h
index f45f725170a6c31a2a5a6f20e7eb3c6c1ac67920..d2e5435a102cfa851aa3d9c81da2f4779050f79e 100644
--- a/chrome/browser/chromeos/chrome_browser_main_chromeos.h
+++ b/chrome/browser/chromeos/chrome_browser_main_chromeos.h
@@ -26,6 +26,7 @@ namespace chromeos {
 class DataPromoNotification;
 class EventRewriter;
 class EventRewriterController;
+class ExtensionSystemEventObserver;
 class IdleActionWarningObserver;
 class LoginLockStateNotifier;
 class LowDiskNotification;
@@ -68,6 +69,8 @@ class ChromeBrowserMainPartsChromeos : public ChromeBrowserMainPartsLinux {
 
  private:
   std::unique_ptr<default_app_order::ExternalLoader> app_order_loader_;
+  std::unique_ptr<ExtensionSystemEventObserver>
+      extension_system_event_observer_;
   std::unique_ptr<PeripheralBatteryObserver> peripheral_battery_observer_;
   std::unique_ptr<PowerPrefs> power_prefs_;
   std::unique_ptr<LoginLockStateNotifier> login_lock_state_notifier_;