Add signal handler for low disk notification

chromeos/dbus/mock_cryptohome_client.h

Index: chromeos/dbus/mock_cryptohome_client.h
diff --git a/chromeos/dbus/mock_cryptohome_client.h b/chromeos/dbus/mock_cryptohome_client.h
index 35b683b628be4298e64d417f08860e216137b96c..1cae4f3b1ca611b5e44dfacf315b82b9a71ebc52 100644
--- a/chromeos/dbus/mock_cryptohome_client.h
+++ b/chromeos/dbus/mock_cryptohome_client.h
@@ -26,6 +26,8 @@ class MockCryptohomeClient : public CryptohomeClient {
                void(const AsyncCallStatusHandler& handler,
                     const AsyncCallStatusWithDataHandler& data_handler));
   MOCK_METHOD0(ResetAsyncCallStatusHandlers, void());
+  MOCK_METHOD1(SetLowDiskSpaceHandler,
+               void(const LowDiskSpaceHandler& handler));
   MOCK_METHOD1(WaitForServiceToBeAvailable,
                void(const WaitForServiceToBeAvailableCallback& callback));
   MOCK_METHOD1(IsMounted, void(const BoolDBusMethodCallback& callback));