In TranslatorHLSL a number of AST simplifications are done, that must
happen in a precise order for things to be correct:
 - First for-loops must be split
 - Then multideclarations must be split
 - Finally comma operators must be split

This adds tests for interaction between this passes to make sure they
are done in the right order.

BUG=668028

Change-Id: I306915b51011bb5467d117352becfd60cbe77be4
Reviewed-on: https://chromium-review.googlesource.com/417989
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>