std::tuple currently isn't available on Chromium/OSX.

BUG=angle:773

Change-Id: I9f9efc88dcfe904e98a76df8b04086b88f724424
Reviewed-on: https://chromium-review.googlesource.com/238442Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>