Migrate ArcBridgeService::Observer and ArcSession::Observer.

components/arc/test/fake_arc_session.cc

Index: components/arc/test/fake_arc_session.cc
diff --git a/components/arc/test/fake_arc_session.cc b/components/arc/test/fake_arc_session.cc
index 5ebc1e04a0214e260cf8287c51f339647aebdf23..7662e6d62150c9addfbdaedce57973b6ed81d2d7 100644
--- a/components/arc/test/fake_arc_session.cc
+++ b/components/arc/test/fake_arc_session.cc
@@ -26,20 +26,20 @@ void FakeArcSession::Start() {
 }
 
 void FakeArcSession::Stop() {
-  StopWithReason(ArcBridgeService::StopReason::SHUTDOWN);
+  StopWithReason(ArcSessionObserver::StopReason::SHUTDOWN);
 }
 
 void FakeArcSession::OnShutdown() {
-  StopWithReason(ArcBridgeService::StopReason::SHUTDOWN);
+  StopWithReason(ArcSessionObserver::StopReason::SHUTDOWN);
 }
 
-void FakeArcSession::StopWithReason(ArcBridgeService::StopReason reason) {
+void FakeArcSession::StopWithReason(ArcSessionObserver::StopReason reason) {
   for (auto& observer : observer_list_)
     observer.OnStopped(reason);
 }
 
 void FakeArcSession::EnableBootFailureEmulation(
-    ArcBridgeService::StopReason reason) {
+    ArcSessionObserver::StopReason reason) {
   DCHECK(!boot_failure_emulation_enabled_);
   DCHECK(!boot_suspended_);