Remove few redundant ImmutableString to std::string conversions Maybe removes few strlen calls. Bug: angleproject:8614 Change-Id: I4fbb5f6abb8e8d21ff44a34975bab379127a0a11 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5372715 Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com> Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>