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/203452Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Nicolas Capens <nicolascapens@chromium.org>