Add ArcEnabled policy implementation

chromeos/dbus/fake_session_manager_client.h

Index: chromeos/dbus/fake_session_manager_client.h
diff --git a/chromeos/dbus/fake_session_manager_client.h b/chromeos/dbus/fake_session_manager_client.h
index 4150091e321cfc2d17ad1d852f6b0fff5613e077..e5b594a1b6ec2e33c6557261dd7be57380f04380 100644
--- a/chromeos/dbus/fake_session_manager_client.h
+++ b/chromeos/dbus/fake_session_manager_client.h
@@ -105,6 +105,8 @@ class FakeSessionManagerClient : public SessionManagerClient {
     return notify_lock_screen_dismissed_call_count_;
   }
 
+  void set_arc_available(bool available) { arc_available_ = available; }
+
  private:
   std::string device_policy_;
   std::map<cryptohome::Identification, std::string> user_policies_;
@@ -117,6 +119,8 @@ class FakeSessionManagerClient : public SessionManagerClient {
   int notify_lock_screen_shown_call_count_;
   int notify_lock_screen_dismissed_call_count_;
 
+  bool arc_available_;
+
   DISALLOW_COPY_AND_ASSIGN(FakeSessionManagerClient);
 };