With certain selection statements with a vertex input in the
condition and side-effects in the else-block, we'd run in to
a D3D9 compiler bug which would cause incorrect results.

We can work around this bug in D3D9 by selectively rewriting
these statements to not use an else clause.

BUG=322794

Change-Id: I93c96fb201ff4959c00d9a36321faac7e0343278
Reviewed-on: https://chromium-review.googlesource.com/184021Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Commit-Queue: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>