This allows us to return different operators from single
declarations, which will be useful for treating invariant
declarations as different operators.

BUG=angle:711

Change-Id: Id278b91854bbefe8e635380d7b27198198236fef
Reviewed-on: https://chromium-review.googlesource.com/212939Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>