This hits an unimplemented feature in Clang. Work around this by using
values instead of references.

BUG=angleproject:1160

Change-Id: I94b08d8fd9a09bbbfbe4bcd1b6f9d7f0031ce18d
Reviewed-on: https://chromium-review.googlesource.com/308910Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>