Ensure that conditional blocks and loop bodies are sequence nodes AST transformations such as unfolding logical operations can only create nodes inside sequence (block) nodes. This patch ensures that these AST transformations work even inside conditional blocks and loop bodies that were first parsed as single statements instead of blocks. BUG=angleproject:971 TEST=WebGL conformance tests Change-Id: If98cb7be653ec7b005537b89547f4f4cf1c07c72 Reviewed-on: https://chromium-review.googlesource.com/272141 Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>