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

Change-Id: I83661f7db82336f3817114eec96a98bc2d395b87
Reviewed-on: https://chromium-review.googlesource.com/187846Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/189081Reviewed-by: Shannon Woods <shannonwoods@chromium.org>