Add caps files for metal

Bug: skia:
Change-Id: I8e7488320d4237cf67d6ebeaad319d3de75b67e6
Reviewed-on: https://skia-review.googlesource.com/27741
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 3db9acc..49e3361 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -581,6 +581,8 @@
 
 skia_metal_sources = [
   "$_include/gpu/mtl/GrMtlTypes.h",
+  "$_src/gpu/mtl/GrMtlCaps.h",
+  "$_src/gpu/mtl/GrMtlCaps.mm",
   "$_src/gpu/mtl/GrMtlGpu.h",
   "$_src/gpu/mtl/GrMtlGpu.mm",
   "$_src/gpu/mtl/GrMtlTrampoline.h",