Now temporary ids are always only created for a specific temporary
variable.

BUG=angleproject:2267
TEST=angle_unittests

Change-Id: Icbd369695abc166ef399bed9ae11a3669f1e7228
Reviewed-on: https://chromium-review.googlesource.com/816951Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>