arc: Handle default app not availble case.

components/arc/test/fake_app_instance.h

Index: components/arc/test/fake_app_instance.h
diff --git a/components/arc/test/fake_app_instance.h b/components/arc/test/fake_app_instance.h
index eeaac8d68324060b73c7ca1bf35150f1ab03fdb0..4557cad5739472ace60ddaf2bfd3100ae6dabe07 100644
--- a/components/arc/test/fake_app_instance.h
+++ b/components/arc/test/fake_app_instance.h
@@ -135,6 +135,10 @@ class FakeAppInstance : public mojom::AppInstance {
   void SendPackageAdded(const mojom::ArcPackageInfo& package);
   void SendPackageUninstalled(const std::string& pacakge_name);
 
+  void SendInstallationStarted(const std::string& package_name);
+  void SendInstallationFinished(const std::string& package_name,
+                                bool success);
+
   int refresh_app_list_count() const { return refresh_app_list_count_; }
 
   const std::vector<std::unique_ptr<Request>>& launch_requests() const {