Fall back to non mipped Texture when we can't copy base to mipped texture

TBR: bsalomon@google.com
Bug: skia:7094
Change-Id: I9d2ba78c4d4332a22e2357cde0598de51299067d
Reviewed-on: https://skia-review.googlesource.com/53541
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/mtl/GrMtlCaps.h b/src/gpu/mtl/GrMtlCaps.h
index 9590bb9..b793159 100644
--- a/src/gpu/mtl/GrMtlCaps.h
+++ b/src/gpu/mtl/GrMtlCaps.h
@@ -39,6 +39,10 @@
         }
     }
 
+    bool isConfigCopyable(GrPixelConfig config) const override {
+        return true;
+    }
+
     bool canConfigBeImageStorage(GrPixelConfig) const override { return false; }
 
 #if 0