This raw node stores text strings that we directly copy to the
output. This allows for more tricky substitutions that don't fit
in to the HLSL/GLSL shared parsing model.

BUG=346463
BUG=391697

Change-Id: Ibbde6db4fc98ef6d892f219631ca1a258a902a86
Reviewed-on: https://chromium-review.googlesource.com/206823Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/207833