Simplify ArcServiceManager by stop deriving it from ArcIntentHelperObserver

chrome/browser/chromeos/arc/arc_service_launcher.cc

Index: chrome/browser/chromeos/arc/arc_service_launcher.cc
diff --git a/chrome/browser/chromeos/arc/arc_service_launcher.cc b/chrome/browser/chromeos/arc/arc_service_launcher.cc
index af50b1aefb23c3b74277b7d3b4c1ce583a3f6c7d..a6e99cf408543cf34bd86528d0086c5f8a83aff3 100644
--- a/chrome/browser/chromeos/arc/arc_service_launcher.cc
+++ b/chrome/browser/chromeos/arc/arc_service_launcher.cc
@@ -102,9 +102,10 @@ void ArcServiceLauncher::Initialize() {
   auto intent_helper = base::MakeUnique<ArcIntentHelperBridge>(
       arc_bridge_service, arc_service_manager_->icon_loader(),
       arc_service_manager_->activity_resolver());
-  // We don't have to remove observer since
-  // ArcServiceManager always outlives ArcIntentHelperBridge.
-  intent_helper->AddObserver(arc_service_manager_.get());
+  // We don't have to call ArcIntentHelperBridge::RemoveObserver() in
+  // ~ArcServiceManager() since the observer in ArcServiceManager always
+  // outlives the ArcIntentHelperBridge object.
+  intent_helper->AddObserver(arc_service_manager_->intent_helper_observer());
   arc_service_manager_->AddService(std::move(intent_helper));
   arc_service_manager_->AddService(
       base::MakeUnique<ArcImeService>(arc_bridge_service));