added TextureRenderTarget to Metal gpu backend

Bug: skia:
Change-Id: I5cacdb832deefe0f8d8460ff10b2216d5dec1ed7
Reviewed-on: https://skia-review.googlesource.com/137890
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Timothy Liang <timliang@google.com>
diff --git a/src/gpu/mtl/GrMtlTexture.h b/src/gpu/mtl/GrMtlTexture.h
index f750832..57a7ee5 100644
--- a/src/gpu/mtl/GrMtlTexture.h
+++ b/src/gpu/mtl/GrMtlTexture.h
@@ -40,7 +40,7 @@
     }
 
 protected:
-    GrMtlTexture(GrMtlGpu*, const GrSurfaceDesc&);
+    GrMtlTexture(GrMtlGpu*, const GrSurfaceDesc&, id<MTLTexture>, GrMipMapsStatus);
 
     GrMtlGpu* getMtlGpu() const;