Metal: use injectAsmStatementIntoLoopBodies on iOS The setting should be enabled for iOS. Bug: chromium:1513738 Change-Id: I5efd4126711eff6df8f5d84689f7f3310d7e8487 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5788428 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com>