translator: Fix use-after-free with DepthRange. Because this builtin uses a structure, certain shaders could trigger the mangled name to be allocated during normal shader compilation. Then when the scope is popped, the mangled name for DepthRange is freed, and we're left with a dangling pointer. Fix this temporarily by enforcing mangled name construction when we initialize the builtins, but we should look for a more robust and future-proof fix. BUG=620937 Change-Id: If130c8b48a18054502abaec08f10264f282b4925 Reviewed-on: https://chromium-review.googlesource.com/354494 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Antoine Labour <piman@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>