Metal: Upstream clear performance fix Restricts in-flight render passes per command buffer a predefined limit. The goal is to reduce the number of active render passes on the system at any one time. Patch is from: https://bugs.webkit.org/show_bug.cgi?id=234008 Bug: angleproject:7386 Change-Id: I6712bf38722e2685ed7d21f12ed0a680779b7a41 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3685190 Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Gregg Tavares <gman@chromium.org>