switched gl_Position and gl_PointSize to sk_*

Bug: skia:
Change-Id: Ie7508991aa975c1400bac23ae49d81041a313968
Reviewed-on: https://skia-review.googlesource.com/51320
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/ast/SkSLASTInterfaceBlock.h b/src/sksl/ast/SkSLASTInterfaceBlock.h
index d445ae0..17f180a 100644
--- a/src/sksl/ast/SkSLASTInterfaceBlock.h
+++ b/src/sksl/ast/SkSLASTInterfaceBlock.h
@@ -16,9 +16,9 @@
 /**
  * An interface block, as in:
  *
- * out gl_PerVertex {
- *   layout(builtin=0) float4 gl_Position;
- *   layout(builtin=1) float gl_PointSize;
+ * out sk_PerVertex {
+ *   layout(builtin=0) float4 sk_Position;
+ *   layout(builtin=1) float sk_PointSize;
  * };
  */
 struct ASTInterfaceBlock : public ASTDeclaration {