GTK L&F: The windows title bar have two window control buttons and there is no maximize control

Testsuite name: Swing manual
Test name(s): Swing_AllComponents/Manual/LAFTests/JFrameLAFTest
Product(s) tested:OracleJDK13b25(64bit)/tonga-4.0.2-rc2
OS/architecture:ubuntu19.04-x64
option: -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel

Actual behavior:
1.step4:The windows title bar have two window control buttons and there is no maximize control.Refer to JFrameLAFTest-base13b24.jpg
2.The test failed as the same issue on ubuntu19.04-x64/OracleJDK13b25 without the option.
3.The test failed as the same issue on ubuntu18.04-x64/OracleJDK13b25 with the same option.