This is to support the upcoming `precise` keyword.

Bug: angleproject:3569
Change-Id: Idbcc8fd6f261757dbbf81b381e7a2dae938d8101
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1947451Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>