Pass the attribute map to egl::Sync::initialize. The attribute map was typically passed to the impl objects in the constructors. Instead, pass it to the initialize function. This removes the need for many member variables in different backends and opens up the future optimization of re-using sync objects by calling initialize on them with new attributes. Bug: angleproject:8430 Change-Id: If69970462cfed39d9a205034adb5ddd937c5ea31 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5063335 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>