Validate empty statements in switch statements Even an empty statement like ";" is a statement according to the grammar. They should not be allowed in switch statements before the first case statement, but on the other hand a switch statement that has just an empty statement after the last statement is valid. Now the parser creates AST nodes from empty statements so that we can validate switch statements correctly. However, they are pruned shortly after parsing completes in PruneNoOps, so they don't affect further processing of the AST. BUG=angleproject:2181 TEST=angle_unittests Change-Id: I1085056fc34b146142546fc5f2b7f3124b910ab9 Reviewed-on: https://chromium-review.googlesource.com/743621 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>