In functions with return types where we would use if-else rewriting,
we would potentially generate a spurious HLSL error that warned of
branches with no return value in the function.

This was causing a maps regression where overlays would not draw
in Earth mode.

BUG=346463
BUG=391697

Change-Id: I9f4fa959057a3a2dab6cdd98f8381b5871cabf03
Reviewed-on: https://chromium-review.googlesource.com/206824Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>