Fix standalone variable shadowing warning. Introduced in https://chromium-review.googlesource.com/362641 Eventually we'll switch to using the same sets of warnings for standalone and GN ANGLE. BUG=angleproject:1441 Change-Id: I6534b9f85b952ddf1d953342cf9c8ddc5de6614e Reviewed-on: https://chromium-review.googlesource.com/362780 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>