This CL adds tests for the NopStatement AST node. Bug: tint:11 Change-Id: I890b7f6bc6347ba4f5a67334385feffd24079d5d Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16665 Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>