Add GrMtlTexture classes

Adds support for basic Texture creation.

Bug: skia:
Change-Id: I9a3f15bef1c88054c19e952e231cad94ad69f296
Reviewed-on: https://skia-review.googlesource.com/30781
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 9bd28e1..e9b33ed 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -585,6 +585,8 @@
   "$_src/gpu/mtl/GrMtlCaps.mm",
   "$_src/gpu/mtl/GrMtlGpu.h",
   "$_src/gpu/mtl/GrMtlGpu.mm",
+  "$_src/gpu/mtl/GrMtlTexture.mm",
+  "$_src/gpu/mtl/GrMtlTexture.h",
   "$_src/gpu/mtl/GrMtlTrampoline.h",
   "$_src/gpu/mtl/GrMtlTrampoline.mm",
   "$_src/gpu/mtl/GrMtlUtil.h",