Implement a dbus client for CupsTool.

chromeos/dbus/dbus_thread_manager.h

Index: chromeos/dbus/dbus_thread_manager.h
diff --git a/chromeos/dbus/dbus_thread_manager.h b/chromeos/dbus/dbus_thread_manager.h
index 5f1ab827f4adb8d1c65eeaa2e8be85c1dd5a43b8..b82e27493bd862855feb8568fdbe2259f9d51011 100644
--- a/chromeos/dbus/dbus_thread_manager.h
+++ b/chromeos/dbus/dbus_thread_manager.h
@@ -30,6 +30,7 @@ class ArcObbMounterClient;
 class CrasAudioClient;
 class CrosDisksClient;
 class CryptohomeClient;
+class CupsClient;
 class DBusThreadManagerSetter;
 class DebugDaemonClient;
 class EasyUnlockClient;
@@ -104,6 +105,7 @@ class CHROMEOS_EXPORT DBusThreadManager {
   CrasAudioClient* GetCrasAudioClient();
   CrosDisksClient* GetCrosDisksClient();
   CryptohomeClient* GetCryptohomeClient();
+  CupsClient* GetCupsClient();
   DebugDaemonClient* GetDebugDaemonClient();
   EasyUnlockClient* GetEasyUnlockClient();
   GsmSMSClient* GetGsmSMSClient();
@@ -168,6 +170,7 @@ class CHROMEOS_EXPORT DBusThreadManagerSetter {
   void SetCrasAudioClient(std::unique_ptr<CrasAudioClient> client);
   void SetCrosDisksClient(std::unique_ptr<CrosDisksClient> client);
   void SetCryptohomeClient(std::unique_ptr<CryptohomeClient> client);
+  void SetCupsClient(std::unique_ptr<CupsClient> client);
   void SetDebugDaemonClient(std::unique_ptr<DebugDaemonClient> client);
   void SetEasyUnlockClient(std::unique_ptr<EasyUnlockClient> client);
   void SetLorgnetteManagerClient(