Add new SkImage factory to create from GrBackendTexture with SkColorType

Bug: skia:
Change-Id: I46bdc54b6d9cdacc8f5a06644aa6b110837879f0
Reviewed-on: https://skia-review.googlesource.com/84342
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/mtl/GrMtlCaps.h b/src/gpu/mtl/GrMtlCaps.h
index 3f2adf8..bc8aac9 100644
--- a/src/gpu/mtl/GrMtlCaps.h
+++ b/src/gpu/mtl/GrMtlCaps.h
@@ -57,6 +57,10 @@
     }
 
 private:
+    bool onValidateBackendTexture(GrBackendTexture* tex, SkColorType ct) const override {
+        return false;
+    }
+
     void initFeatureSet(MTLFeatureSet featureSet);
 
     void initGrCaps(const id<MTLDevice> device);