tst_qquickrectangle::gradient_separate() is flaky.

agent:2019/01/18 19:53:00 build.go:449: Executing instruction 337 of 484 - RunQtUnitTest
agent:2019/01/18 19:53:00 build.go:314: [make check -j1] 900 900
agent:2019/01/18 19:53:00 build.go:192: /home/qt/work/qt/qtdeclarative/tests/auto/quick/qquickrectangle/target_wrapper.sh  ./tst_qquickrectangle -o /home/qt/work/testresults/tests/auto/quick/qquickrectangle211007622,xml -o -,txt
agent:2019/01/18 19:53:00 build.go:192: ********* Start testing of tst_qquickrectangle *********
agent:2019/01/18 19:53:00 build.go:192: Config: Using QtTest library 5.12.2, Qt 5.12.2 (x86_64-little_endian-lp64 shared (dynamic) debug build; by GCC 7.3.1 20180323 [gcc-7-branch revision 258812])
agent:2019/01/18 19:53:00 build.go:192: PASS   : tst_qquickrectangle::initTestCase()
agent:2019/01/18 19:53:00 build.go:192: PASS   : tst_qquickrectangle::color()
agent:2019/01/18 19:53:00 build.go:192: PASS   : tst_qquickrectangle::gradient()
agent:2019/01/18 19:53:01 build.go:192: PASS   : tst_qquickrectangle::gradient_border()
agent:2019/01/18 19:53:01 build.go:192: QWARN  : tst_qquickrectangle::gradient_separate() QSGThreadedRenderLoop: expose event received for window QQuickView(0x7ffce364b2a0 exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window), geometry=0,0 0x0) with invalid geometry: QRect(0,0 0x0) on QScreen(0x21c19e0, name=Virtual-1)
agent:2019/01/18 19:53:01 build.go:192: QWARN  : tst_qquickrectangle::gradient_separate() QSGThreadedRenderLoop: expose event received for window QQuickView(0x7ffce364b2a0 exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window), geometry=0,0 0x0) with invalid geometry: QRect(0,0 0x0) on QScreen(0x21c19e0, name=Virtual-1)
agent:2019/01/18 19:53:01 build.go:192: FAIL!  : tst_qquickrectangle::gradient_separate() '!isDirty' returned FALSE. ()
agent:2019/01/18 19:53:01 build.go:192:    Loc: [tst_qquickrectangle.cpp(138)]
agent:2019/01/18 19:53:01 build.go:192: PASS   : tst_qquickrectangle::gradient_multiple()
agent:2019/01/18 19:53:01 build.go:192: QWARN  : tst_qquickrectangle::gradient_preset() file:///home/qt/work/qt/qtdeclarative/tests/auto/quick/qquickrectangle/data/gradient-preset.qml:12:5: QML Rectangle: No such gradient preset '-1'
agent:2019/01/18 19:53:01 build.go:192: PASS   : tst_qquickrectangle::gradient_preset()
agent:2019/01/18 19:53:01 build.go:192: PASS   : tst_qquickrectangle::antialiasing()
agent:2019/01/18 19:53:01 build.go:192: PASS   : tst_qquickrectangle::cleanupTestCase()
agent:2019/01/18 19:53:01 build.go:192: Totals: 8 passed, 1 failed, 0 skipped, 0 blacklisted, 493ms
agent:2019/01/18 19:53:01 build.go:192: ********* Finished testing of tst_qquickrectangle *********
agent:2019/01/18 19:53:01 build.go:192: Makefile:339: recipe for target 'check' failed
agent:2019/01/18 19:53:01 build.go:192: make: *** [check] Error 1