Add work-around for D3D9 shader compiler bug. 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 use an 'else if' clause instead of 'else'. BUG=322794 Change-Id: I93c96fb201ff4959c00d9a36321faac7e0343278 Reviewed-on: https://chromium-review.googlesource.com/184681 Reviewed-by: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>