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>
diff --git a/src/compiler/translator/SymbolTable.h b/src/compiler/translator/SymbolTable.h
index 673bf0e..6d9b714 100644
--- a/src/compiler/translator/SymbolTable.h
+++ b/src/compiler/translator/SymbolTable.h
@@ -347,6 +347,9 @@
                                  const char *name,
                                  const TType &type);
     TVariable *insertStructType(ESymbolLevel level, TStructure *str);
+    TInterfaceBlockName *insertInterfaceBlockNameExt(ESymbolLevel level,
+                                                     const char *ext,
+                                                     const TString *name);
 
     bool insertConstInt(ESymbolLevel level, const char *name, int value, TPrecision precision)
     {