Produce constructors instead of conversions. GLSL only supports explicit conversion through constructors. Therefore the conversion nodes are redundant. BUG=380353 Change-Id: Id871c34750191dac431bf72aac9afed7b0db7f8e Reviewed-on: https://chromium-review.googlesource.com/203452 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Nicolas Capens <nicolascapens@chromium.org>