arc: Abort booting ARC if the device is critically low on disk space.

chromeos/dbus/fake_cryptohome_client.h

Index: chromeos/dbus/fake_cryptohome_client.h
diff --git a/chromeos/dbus/fake_cryptohome_client.h b/chromeos/dbus/fake_cryptohome_client.h
index 02dece263f323ff5a71e36b183925ef21a9d9f0b..2701e86d7df82abaafcb03474c64c97d1ea78c54 100644
--- a/chromeos/dbus/fake_cryptohome_client.h
+++ b/chromeos/dbus/fake_cryptohome_client.h
@@ -44,6 +44,7 @@ class CHROMEOS_EXPORT FakeCryptohomeClient : public CryptohomeClient {
                         const ProtobufMethodCallback& callback) override;
   void GetAccountDiskUsage(const cryptohome::Identification& account_id,
                            const ProtobufMethodCallback& callback) override;
+  void GetFreeDiskSpace(const GetFreeDiskSpaceCallback& callback) override;
   void GetSystemSalt(const GetSystemSaltCallback& callback) override;
   void GetSanitizedUsername(const cryptohome::Identification& cryptohome_id,
                             const StringDBusMethodCallback& callback) override;