Metal: Fix Hang in WebGL CTS Occlusionquery_strict test If a query was just in progress and then we switch contexts a command buffer, which has already been enqueued, is not committed. Later, other command buffers are enqueued and committed and Metal hangs, waiting on the uncommitted but previously enqueued command buffer. The solution was to not enqueue a command buffer early but instead, enqueue just before committing. Bug: angleproject:6752 Change-Id: I62c07ca3d1ed98cc5b27c8c4af405fdedff922b8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3461419 Reviewed-by: Kyle Piddington <kpiddington@apple.com> Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Gregg Tavares <gman@chromium.org>