Tests: Fix EGLContextSharingTestNoFixture.SwapBuffersShared. Sometimes `swapThread` may finish until `renderThread` wait for `Step::TextureInitialized` step. In this situation `swapThread` will change `currentStep` to `Abort` in the `ThreadSynchronization<>` destructor, causing wait for `Step::TextureInitialized` to fail. Bug: angleproject:6851 Change-Id: Ib08b6de11873e9959eaa810bcf8cb404c95c80d4 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4381626 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Igor Nazarov <i.nazarov@samsung.com>