Metal: Validate max render target size without an allocation We would allocate a MTLRenderPassDescriptor for validating an internal error case only to throw it away immediately afterwards. This happened on every new render pass. This allocation/release amounts to about 10% of ANGLE's CPU time when running Chrome. Bug: chromium:1466696 Change-Id: I0bbe086c0b8006d2ff15ae57f25b591f791acb60 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4706925 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>