ES31: Implement gl_in in Geometry Shader This patch intends to implement geometry shader built-in interface block instance gl_in defined in GL_OES_geometry_shader. 1. Add the definition of gl_in and its interface block gl_PerVertex into the symbol table. 2. Support gl_Position as a member of gl_in. 3. Set the array size of gl_in when a valid input primitive type is known. 4. Add check that it should be a compile error to index gl_in or call length() on gl_in without a valid input primitive declaration. This patch also adds unit tests to cover all these new features. BUG=angleproject:1941 TEST=angle_unittests Change-Id: I8da20c943b29c9ce904834625b396aab6302e1e1 Reviewed-on: https://chromium-review.googlesource.com/605059 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>