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

Change-Id: Icd53023286dfa43b653fd6e261b1cdb952627706
Reviewed-on: https://chromium-review.googlesource.com/187847Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>