Also known as nameless structs. Uniform structs without a struct name
would not be parsed correctly. This fixes the bug by adding a tree
transformation. The transformation gives an internally scoped name to
the embedded struct.

Bug: angleproject:2665
Change-Id: I43e4dad7d9ad64a40e382066bb136e4f8f719797
Reviewed-on: https://chromium-review.googlesource.com/1101566Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>