login: use same observer list policy in real and fake concierge client

This change is needed to ensure that fake behaves the same as real
client and we can use it in the unit test to validate that arc
instance stopped is not fired on unrelated instance.

BUG=b:164816080
TEST=cq

Change-Id: Ice5e588b81231ac87b78dafd25188d6629b38bd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2469231
Auto-Submit: Muhammad Hasan Khan <mhasank@chromium.org>
Commit-Queue: Muhammad Hasan Khan <mhasank@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816907}

chromeos/dbus/concierge_client.cc

@@ -428,13 +428,13 @@ class ConciergeClientImpl : public ConciergeClient {
   dbus::ObjectProxy* concierge_proxy_ = nullptr;
 
   base::ObserverList<Observer> observer_list_{
-      base::ObserverListPolicy::EXISTING_ONLY};
+      ConciergeClient::kObserverListPolicy};
   base::ObserverList<VmObserver>::Unchecked vm_observer_list_{
-      base::ObserverListPolicy::EXISTING_ONLY};
+      ConciergeClient::kObserverListPolicy};
   base::ObserverList<ContainerObserver>::Unchecked container_observer_list_{
-      base::ObserverListPolicy::EXISTING_ONLY};
+      ConciergeClient::kObserverListPolicy};
   base::ObserverList<DiskImageObserver>::Unchecked disk_image_observer_list_{
-      base::ObserverListPolicy::EXISTING_ONLY};
+      ConciergeClient::kObserverListPolicy};
 
   bool is_vm_started_signal_connected_ = false;
   bool is_vm_stopped_signal_connected_ = false;

chromeos/dbus/concierge_client.h

@@ -21,6 +21,9 @@ namespace chromeos {
 // start and stop VMs, as well as for disk image management.
 class COMPONENT_EXPORT(CHROMEOS_DBUS) ConciergeClient : public DBusClient {
  public:
+  static constexpr base::ObserverListPolicy kObserverListPolicy =
+      base::ObserverListPolicy::EXISTING_ONLY;
+
   // Used for observing Concierge service itself.
   class Observer : public base::CheckedObserver {
    public:

chromeos/dbus/fake_concierge_client.h

@@ -332,13 +332,17 @@ class COMPONENT_EXPORT(CHROMEOS_DBUS) FakeConciergeClient
   std::vector<vm_tools::concierge::DiskImageStatusResponse>
       disk_image_status_signals_;
 
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer> observer_list_{
+      ConciergeClient::kObserverListPolicy};
 
-  base::ObserverList<VmObserver>::Unchecked vm_observer_list_;
+  base::ObserverList<VmObserver>::Unchecked vm_observer_list_{
+      ConciergeClient::kObserverListPolicy};
 
-  base::ObserverList<ContainerObserver>::Unchecked container_observer_list_;
+  base::ObserverList<ContainerObserver>::Unchecked container_observer_list_{
+      ConciergeClient::kObserverListPolicy};
 
-  base::ObserverList<DiskImageObserver>::Unchecked disk_image_observer_list_;
+  base::ObserverList<DiskImageObserver>::Unchecked disk_image_observer_list_{
+      ConciergeClient::kObserverListPolicy};
 
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.